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GEISTEEAL    PHYSIOLOGY 


MUSCLES  AND  NERVES. 


BY 

De.   I.   ROSENTHAL, 

PROFESSOR   OF   PHYSIOLOGY   IN    THE    UNITEESITY   OF  ERLANGEN. 


WITH  SEVENTY-FIVE  WOODCUTS. 


NEW  YORK: 

D.    APPLET02^    AND    COMPANY, 

,1,  3,  AXD  5  BOND   STREET. 

1881. 


THIS    BOOK    IS    DEDICATED 

TO 

HIS    VENERATED    MASTER 
EMIL    DU    BOIS-REYMOND 

BY 

THE    AUTHOR 


PEEFACE. 


TfflS  attempt  at  a  connected  account  of  the  General 
Physiology  of  Muscles  and  Nerves  is,  as  far  as  I  know, 
the  first  of  its  kind.  The  necessary  data  for  this 
branch  of  science  have  been  gained  only  within  the 
last  thirty  years,  and  even  now  many  of  the  facts  are 
uncertain  and  have  been  insufficiently  studied.  Under 
these  circumstances  it  might  well  be  asked  if  the  time 
has  yet  come  for  such  an  account  as  this.  But  any- 
one who  endeavours  to  gain  an  idea  of  this  branch  of 
knowledge  from  the  existing  text-books  of  Physiology 
will  probably  labour  in  vain.  Moreover,  the  subject 
is  one  which  has  many  points  of  interest  not  only  for 
the  specialist,  but  also  for  the  physicist,  for  the  psy- 
chologist, and  indeed  for  every  cultivated  man  ;  and  as 
regards  the  gaps  in  our  knowledge,  they  are  scarcely 
greater  than  those  in  any  other  branch  of  the  science 
of  life. 

There  being  no  previous  writers  on  the  same  sub- 
ject, I  have  been  obliged  to  d_  j)end  entirely  on  myself 
in  the  matter  of  the  arrangement,  in  the  selection 
of  important  points  and  the  rejection  of  those  of  less 
importance,  and  as  to  the  form  in  which  the  subject 


Viil  PREFACE. 

is  presented.  From  the  experience  gained  by  teach- 
ing during  more  than  fifteen  years,  I  believe  that  I 
have  acquired  sufficient  clearness  of  expression,  even  in 
treating  of  more  difficult  matters,  to  be  intelligible 
when  studied  carefully  even  by  those  who  are  not 
specialists.  In  certain  cases  it  has  been  impossible  to 
avoid  somewhat  long  explanations  of  physical  and, 
especially,  of  electric  phenomena.  But  these  have 
been  confined  to  the  narrowest  possible  limits,  and  I 
must  refer  those  who  require  further  details  to  my 
EleJctricitdtslehre  fiir  Mediciner  (Berlin,  Hirschwald). 
It  has  also  been  unavoidable  in  giving  an  account  of 
one  branch  of  Physiology  to  indicate  the  connection 
with  other  branches,  though  it  has  been  impossible  to 
enter  into  the  details  of  these.  To  those  who  feel 
inclined  to  follow  these  matters  further,  I  recommend 
the  study  of  Huxley's  '  Elementary  Physiology.'  Cer- 
tain details,  which  would  have  detained  the  course  of 
the  text  too  long,  I  have  relegated  to  the  Notes  and 
Additions  at  the  end  of  the  book. 

In  accordance  with  the  title  of  the  book,  I  have 
omitted  too  scientific  proofs,  references,  &c.  The 
names  of  men  of  science  to  whom  the  discovery  of  the 
facts  is  due  have  only  been  occasionally  introduced. 
In  this  matter  no  fixed  rule  has  been  followed,  but  it 
did  not  seem  right  to  omit  occasional  mention  of  the 
names  of  the  chief  founders  of  this  branch  of  know- 
ledge— Ed.  Weber,  E.  du  Bois-Reymond,  and  H.  Helm- 
holtz. 

Erlaxn^gen:  Ap)-'il  15, 1877. 


CONTENTS. 


PACK 

PREFACE vii 

CHAPTER  I. 

1.  Introduction  :  Motion  and  sensation  as  animal  charac- 
teristics ;  2.  Movement  in  plants;  3.  Molecular  motion; 
4.  Simplicity  of  the  lowest  organisms  ;  5.  Protoplasmic 
motion  and  amoeboid  motion;  6.  Elementary  organisms 
and  gradual  diiferentiation  of  the  tissues ;  7.  Ciliary 
motion  ...........         1 

CHAPTER  II. 

1.  Muscles,  their  form  and  structure;  2.  Minute  structure  of 
striated  muscle-fibres ;  3.  Connection  of  muscles  and 
bones  ;  4.  Bones  and  bone-sockets ;  5.  The  law  of  elasticity: 
6.  The  elasticity  of  the  muscles 12 

CHAPTER  III. 

1.  Irritability  of  muscle;  2.  Contraction  and  tetanus;  3. 
Height  of  elevation  and  performance  of  work ;  4.  Internal 
work  during  tetanus  ;  5.  Generation  of  heat  and  muscle- 
tone  :  G.  Alteration  in  form  during  contraction  ...       28 

CHAPTER  lY. 

1.  Alteration  in  elasticitj' during  contraction;  2.  Duration  of 
contraction ;   the  myograph  ;  3.  Determination  of  electric 


X  CONTENTS. 

PAGE 

time ;  4.  Application  of  this  to  muscular  pulsation  ;  5. 
Burden  and  over-burden,  muscular  force  ;  6.  Determina- 
tion of  muscular  force  in  man  ;  7.  Alteration  in  muscular 
force  during  contraction       .......       47 

CHAPTER  V. 

1.  Chemical  processes  within  the  muscle  ;  2.  Generation  of 
warmth  during  contraction  ;  3.  Exhaustion  and  recovery  ; 
4.  Source  of  muscle-force  ;  5.  Death  of  the  muscle  ;  6. 
Death-stiifening  (^Higor  mortis) 72 

CHAPTER  VI. 

J.  Forms  of  muscle  ;  2.  Attachment  of  muscles  to  the  bones ;  .3. 
Elastic  tension;  4.  Smooth  muscle-fibres;  5.  Peristaltic 
motion  ;  6.  Voluntary  and  involuntary  motion    ...       91 

CHAPTER  YII. 

1.  Nerve-fibres  and  nerve-cells  ;    2.  Irritability  of  nerve -fibre; 

3.  Transmission  of  the  irritation ;  4.  Isolated  transmis- 
sion ;  5.  Irritability ;  6.  The  curve  of  irritation ;  7.  Ex- 
haustion and  recovery,  death 103 

CHAPTER  YIII. 

1.  Electrotonus ;  2.  Modifications  of  excitability ;  3.  Law  of 
pulsations;  4.  Connection  of  electrotonus  with  excita- 
bility; 5.  Condition  of  excitability  in  electrotonus;  6. 
Explanation  of  the  law  of  pulsations;  7.  General  law  of 
nerve-excitement  . 125 

CHAPTER  IX. 

1.  Eleciric  phenomena;  2.  Electric  fishes  ;  3.  Electric  organs  ; 

4.  Multiplier  and  tangent  galvanometer ;  5.  Ditficulty  of 
the  study  ;  6.  Homogeneous  diverting  vessels;  7.  Electro- 
motive force  ;  8.  Electric  fall ;  9.  Tension  in  the  closing 
arch 153 


CONTEXTS.  XI 

CHAPTER  X. 

PAGE 

1.  Diverting  arches;  2.  Current-curves  and  tension-curves; 
3.  Diverting  cylinders;  4.  Method  of  measuring  tension 
differences  by  compensation 17G 

CHAPTER  XI. 

1.  A  regular  muscle-prism;  2.  Currents  and  tensions  in  a 
muscle-prism ;  3.  Muscle-rhombus ;  4.  IiTegnlar  muscle- 
rhombi ;  5.  ViiTrent  oi  m.  ffasti'ocnemius      ....     189 


CHAPTER  XII. 

Negative  variation  of  the  muscle-current ;  2.  Living  muscle 
is  alone  electrically  active  ;  3.  Parelectronomy  ;  4.  Secon- 
dary pulsation  and  secondary  tetanus  ;  5.  Glands  and  their 
currents         .......  ...     202 


CHAPTER  XIII. 

1.  The  nerve-current;  2.  Negative  variation  of  the  nerve- 
current;  3.  Duplex  transmission  in  the  nerve  ;  4.  Kate  of 
propagation  of  negative  variation ;  5.  Electrotonus ;  6. 
Electric  tissue  of  electric  fishes;  7.  Electric  action  in  plants     215 

CHAPTER  XIV. 

1.  General  summary ;  2.  Fundamental  principles ;  3.  Com- 
parison of  muscle-prism  and  magnet;  4.  Explanation  of 
the  tensions  in  muscle-prisms  and  muscle-rhombi ;  5. 
Explanation  of  negative  variation  and  parelectronomy;  6. 
Application  to  nerves ;  7.  Application  to  electric  organs 
and  glands 226 

CHAPTER  XT, 

1.  Connection  of  nerve  and  muscle  ;  2.  Isolated  excitement  of 
individual  muscle-fibres ;  3.  Discharge-hypothesis ;  4.  Prin- 


XU  CONTENTS. 


PAGE 


ciple  of  the  dispersion  of  forces;  5.  Independent  irrita- 
bility of  muscle-substance;  6.  Curare;  7.  Chemical  irri- 
tants ;  8.  Theory  of  the  activity  of  the  nerves     .         .         .     21i 

CHAPTER  XVI. 

Various  kinds  of  nerves  ;  2.  Absence  of  indicable  differences 
in  the  iibres  ;  3.  Characters  of  nerve-cells  ;  4.  Various  kinds 
of  nerve-cells ;  5.  Voluntary  and  automatic  motion ;  6.  Re- 
flex motion  and  co-relative  sensation ;  7.  Sensation  and 
consciousness ;  8.  Retardation ;  9.  Specific  energies  of 
nerve-cells ;  10.  Conclusion . 261 


NOTES  AND   ADDITIONS. 

1.  Graphical  Representation.     Mathematical  Function  .         .  203 

2.  Irritation  of  Muscle-Fibres,  Height  of  Elevation  and  Per- 

formance of  Work      ........  297 

3.  Excitability   and   Strength  of  Irritant.     Combination  of 

Irritants 299 

•t.  Curve  of  Excitability.     Resistance  to  Transmission        .     .  300 

5.  Influence  of  the  Length  of  Irritated  Portion  of  Nerve       .  303 

6.  Difference  between  closing  and  opening   Inductive    Cur- 

rents.    Helmholtz's  Arrangement  .....  304 

7.  Effect  of  Currents  of  Short  Duration 307 

8.  Unipolar  Irritation 309 

9.  Tangent  Galvanometer 310 

10.  Tensions  in  Conductors        .......  311 

11.  Duplex  Transmission.     Degeneration,  Regeneration,  and 

Healing  of  Bisected  Nerves 312 

12.  Negative  Variation  and  Excitement       ...         .     .  313 

13.  Electrotonus.     Secondary  Pulsations  effected  by  Neives. 

Paradoxical  Pulsation .31-4 

14.  Parelectronomy        .         .         .         .         .         .         .         .     .  31.5 

15.  Discharge  Hj^othesis  and  Isolated  Transmission  in  Nerve- 

Fibre        316 

Index    .        . ,        .    .  319 


LIST   OF  WOODCUTS. 

FIG.  VAQK 

1.  Amoebte 6 

2.  White  Blood-Corpuscles  from  a  Guinea-Pig    .        .         .    .  7 
3a.  Ciliate  Cells  situated  with  the  other  Cells  on  a  Mem- 
brane       .         .         .        .        .        .        .         .         .        .10 

3J.  A  single  Ciliate  Cell,  greatly  magnified,  of    somewhat 

abnormal  form     .         .         .         .         •         .         .         .     .  10 

4.  Striated  Muscle-Fibres 13 

5.  The  Double-headed  Calf-Muscle  (w.  gagtrocncmius)  with 

its  Tendons 17 

6.  The  Bones  of  the  Arm 19 

7.  Du    Bois-lleymond's   Apparatus  for  studying  the  Elastic 

Extension  in  Muscle   ........  25 

8.  The  Simple  M^-ograph 26 

9.  Du  Bois-Reymond's  Muscle-Telegraph 29 

10.  Induction  Coil      .         .         . 31 

11.  Electric  Wheel 33 

12.  Wagner's  Hammer        ........  31 

13.  Du  Bois-Reymond's  Sliding  Inductive  Apparatus    .         .     .  35 

14.  Du  Bois-Reymond"s  Tetanising  Key 36 

15.  Heights  of  Elevation  with  different  Weights  .         .         .     .  38 

16.  The  Changes  in  Elasticity  during  Contraction      ...  48 

17.  Helmholtz's  M3-ograph .62 

IS.  The  Curve  of  Pulsation  of  a  Muscle    .          ....  56 

19.  Jlcasurement   of  small  Angles  of  Deflection  with  Mirror 

and  Lens 57 

20.  Apparatus  for  measuring  the  Duration  of  Muscle-Contrac- 

tion    60 

21.  End  of  the  Lever  of  the  Time-determining  Apparatus  witli 

Capsule  of  Quicksilver 61 

22.  Diagram  of  Experiment  for  measuring  Electric  Time          .  62 

23.  Diagram  of  the  Flexor  Appara' us  of  the  Forearm          .     .  68 

24.  Dyn.amometer       ........         .69 


XIV 


LIST   OF   WOODCUTS. 


25. 
26. 
27. 
28. 
29. 
30. 
31. 

32. 
33. 
34. 
35. 
36. 
37. 
38. 
39. 
40. 
41. 
42. 
43. 
44. 
45. 
46. 
47. 
48. 
49. 
50. 
51. 

52. 
53. 
54. 
55. 
56. 
57 
59. 
60. 
61. 
62. 
63. 

64. 


I'AriK 

Smooth  Muscle-Fibres 97 

Nerve-Fibres         ....,,...  104 

Ganglion-Cells  with  Nerve-Processes  .....  106 
Spring  Myograph  of  E.  du  Bois-Reymond  ,         ,         ,         .112 

Propagation  of  the  Excitement  in  the  Nerve          .         .     .  114 

Elect  rot  onu3 127 

Electrotonus   under  the  influence  of  Currents  of  varying 

Strength 130 

Rheochord 133 

Electrotonus 140 

Series  of  Magnetic  Needles  representing  Nerve-Particles  .  147 

Rheochord 149 

Electric  Current 159 

Multiplier 161 

Reflecting  Galvanometer 163 

Du  Bois-Rcymond"s  homogeneous  Diverting  Vessel     .         .  166 

Distribution  of  Currents  in  Irregular  Conductors    .         .     .  170 

Electric  Fall 172 

Fall  in  different  Wires 173 

Current-Paths  in  a  Conductor 175 

Current- Curves  and  Tension-Curves 178 

Dn  Bois-Reymond's  Diverting  Cylinders      ....  181 

MSasirrement  by  Compensation  of  Differences  in  Tension  .  184 

Du  Bois-Reymond's  Round  Compensator      ....  186 

Diagram  of  Electric  Measurement  by  Round  Compensator  187 

A  Regular  Muscle-Prism 190 

Currents  in  a  Muscle-Prism 192 

Tensions   on  the   Longitudinal   and    Cross  Sections  of  a 

Regular  Muscle-Prism 1 93 

Tensions  in  a  Regular  Muscle-Rhombus           ,         .         .     .  195 

Currents  in  a  Regular  Muscle-Rhombus       ....  196 

Currents  in  the  Gastrocnemius 200 

Muscle-Current  during  Pulsation 203 

Deflection  of  the  Magnetic  Needle  by  the  Will       .         .     .  205 

and  58.  Secondary  Pulsation 210 

Tension  in  Nerves 217 

Changes  in  Tension  during  Electrotonus      ....  220 

Theory  of  Magnetism 230 

Diagram  of  a  Piece  of  Muscle-Fibre 231 

Diagram   of    the   Electric  Action  in  an  Aggregation   of 

Muscle-Elements 233 

Diagram  of  an  obhque  Cross-Section 234 


LIST   OF   WOODCUTS. 


XV 


65.  Magnetic  Induction 

66.  Magnetic  Induction 

67.  Nerve-Terminations  in  the  Muscles  of  a  Guinea-Pi, 

68.  Ganglion-Cells  from  the  Human  Brain 

69.  Graphical  Eepresentation  of  Muscle-Extension 

70.  Representations  of  Positive  and  Negative  Values 

71.  Action  of  Oblique  Muscle-Fibres    . 

72.  The  Sciatic  Nerve  and  Calf- Muscle  of  a  Frog 
7.3.  Duration  of  Inductive  Currents 

74.  Helmholtz"s  Arrangement  with  a  Sliding  Inductive 

tus 

lb  A,  B,  C.  Secondary  Pulsation  from  the  Nerves 


Appara- 


PAGE 

242 
243 
245 
266 
295 
296 
297 
.302 
305 

307 
315 


GENERAL   PHYSIOLOGY 


OP 


MUSGLES    AND    NEEVES, 


otOic 


CHAPTEE    I. 

1..  Introduction : — Movement  and  sensation  as  animal  charac- 
teristics;  2.  Movement  in  plants;  3.  Molecular  movements; 
4.  Simplicity  of  the  lowest  organisms ;  5.  Protoplasmic  and 
amoeboid  movements  ;  6.  Elementary  organisms,  and  the  gradual 
dilfercntiation  of  the  tissues  ;  7.  Ciliary  movement. 

1.  The  student  who  has  elected  to  study  the  pheno- 
mena of  life  probably  meets  with  no  more  attractive,  and 
at  the  same  time  no  harder  task  than  that  of  explaining 
motion  and  sensation.  It  is  especially  in  these  pheno- 
mena that  the  distinction  lies  between  animate  and 
inanimate  objects,  between  animals  and  plants.  It  is 
true  that  movements  can  be  detected  even  in  inanimate 
objects,  and,  indeed,  according  to  the  modem  conception, 
all  natural  phenomena  depend  on  motion,  either  on  that 
of  entire  masses,  or  on  that  of  the  smallest  particles 
of  the  masses.      But  the  movements  of  animals  are 


2  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

of  a  different  kind.  The  contraction  of  a  polyp  when 
touched  and  the  voluntary  movement  of  the  human 
arm  are  phenomena  of  a  peculiar  kind,  and  result  from 
circumstances  qaite  other  than  those  which  cause  the 
fall  of  a  stone  or  the  attraction  and  repulsion  exercised 
between  magnetic  or  electric  masses.  Moreover,  sensa- 
tion, such  as  we  are  conscious  of  in  ourselves,  and  of  the 
existence  of  which  in  other  men  and  in  animals  we  learn 
either  from  the  statements  or  from  the  conduct  of  those 
others,  seems  to  be  entirely  unrepresented  in  inanimate 
nature ;  it  even  appears  doubtful  if  it  occurs  in  plants. 
Upon  this  task,  hard  as  it  is,  physiological  research  has 
thrown  much  light;  it  is  the  knowledge  which  has  thus 
already  been  gained  which  will  form  the  subject  of  the 
following  explanations. 

2.  Although  even  in  plants  movements  occur  similar 
to  those  observable  in  animals,  yet  there  seems  to  be  an 
essential  difference  between  the  two.  For  instance,  in 
most  animals  we  find  that  special  organs  are  formed  to 
serve  principally  for  movement.  Such  are  the  muscles, 
which  form  what  is  ordinarily  called  flesh.  Organs 
of  this  sort  have  never  yet  been  seen  in  plants.  But 
not  all  the  movements  of  the  animal  body  are  accom- 
plished by  the  muscles,  and  some  forms  of  motion  occur 
in  exactly  the  same  way  in  the  plant  as  in  the  animal 
oi'ganism. 

These  movements  are  most  evident,  and  are  most 
easily  explained  in  the  sensitive  plant  (^iMimosa  pudica). 
The  stem  and  branches  of  the  sensitive  plant  bear  leaf- 
stalks, each  of  which  again  bears  secondary  leaf-stalks, 
to  which  latter  the  individual  leaflets  are  attached.  If 
the  plant  is  shaken,  the  leaf-stalks  suddenly  bend  and 
sink,  the  upper  surfaces  of  the  two  halves  of  each  leaflet 


MOLECULAR   MOVEMENTS.  3 

meeting  together  as  do  the  two  halves  of  a  sheet  of 
paper  when  folded.  This  movement  may  be  excited  in 
any  individual  stalk,  most  easily  by  touching  or  softly 
rubbing  the  under  surface  of  that  part  of  it  which  is 
immediately  attached  to  the  branch.  At  this  point  the 
leaf-stalk  is  attached  to  the  branch  by  a  lump-like  thick- 
enings or  node.  Similar  nodes  occur  at  the  bases  both  of 
the  secondary  leaf-stalks  and  of  the  leaflets.  If  one  of 
these  nodes  is  cut  through,  a  bundle  of  fibres  is  observ- 
able in  the  centre,  round  which  there  is  a  layer  of  cells, 
very  full  of  sap,  the  walls  of  which  are  thicker  on  the 
upper,  thinner  on  the  lower  side.  Between  the  cells ' 
are  spaces  filled  with  air.  Now,  it  can  be  shown  that 
the  bending  movement  is  due  to  the  fact  that  part  of 
the  fluid  matter  passes  out  of  the  cells  into  the  inter- 
mediate spaces,  so  that  the  cellular  tissue  becomes  weaker 
9.nd  less  able  to  support  the  stalk. 

Motion  of  this  sort  is,  however,  very  different  from 
the  motion  peculiar  to  animals,  in  that  in  the  latter, 
as  we  shall  presently  see,  it  serves  to  counteract  the 
pressure  of  opposed  weights  ;  while  in  the  Mimosa  the 
pressure  of  the  leaf-stalk  is  do\vnward  when  the  under 
side  of  the  node  becomes  slack.  Before,  however,  we 
examine  minutely  the  motion  peculiar  to  animals,  men- 
tion must  be  made  of  certain  other  phenomena  of 
motion  which  occur  partly  in  the  vegetable,  partly  in 
the  animal  world,  but  which  can  scarcely  be  observed 
without  the  aid  of  the  microscope,  as  the  efficient  forces 
in  these  cases  are  too  slight  to  produce  perceptible 
movements  of  the  larger  parts  of  the  mass. 

3.  Among  these  forms  of  motion  we  do  not  include 
the  so-called  inolecular,  or  Broivnian  movements,  to 
which  the  celebrated  Englisli  botanist  Brown  first  called 


4  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

attention.  If  portions  of  vegetable  or  animal  bodies 
are  observed  under  high  magnifying  powers,  small 
granules  or  similar  bodies  are  seen  to  be  engaged  in  a 
peculiar  tremulous  motion.  Whence  does  this  arise  ? 
That  it  is  not  a  vital  phenomenon  is  sufficiently  shown 
by  the  fact  that  perfectly  inanimate  bodies,  for  instance, 
the  carbon  particles  of  finely  rubbed  Indian  ink,  exhibit 
the  same  movement.  The  effect  is,  in  fact,  due  merely 
to  currents  in  the  fluid,  by  which  the  light  particles 
suspended  in  the  fluid  are  carried  away.  Such  currents 
are  easily  engendered  in  any  fluid,  sometimes  in  con- 
sequence of  uneven  temperature,  sometimes  in  conse- 
quence of  evaporation,  sometimes,  also,  as  the  result  of 
the  unavoidable  shaking  of  the  microscope.  Weak  as 
these  currents  may  be,  the  disturbance  caused  by  them, 
when  seen  under  strong  microscopic  power,  seems  con- 
siderable, and  is  often  hardly  distinguishable  from  those 
movements  which  are  caused  by  the  vital  activities  of 
the  particles.  Sometimes  this  molecular  motion  may 
be  detected  within  parts  of  living  bodies ;  in  which  case 
small  granules  swim  about  in  a  clear  fluid  within  larger 
or  smaller  cavities  in  these  parts  of  living  bodies. 

4.  If  a  drop  of  pond  water  is  placed  under  the 
microscope,  many  living  objects,  some  of  which  shoot 
quickly  about  in  all  directions,  are  usually  discernible 
in  the  water.  Side  by  side  with  these  occur  certain 
oblong,  or  rod-shaped  bodies,  moving  tremulously  about 
with  greater  or  less  rapidity.  It  is  often  hard  to 
distinguish  whether  the  motion  seen  in  these  latter  is 
independent  or  molecular.  It  must  be  observed  whether 
of  these  bodies  two  contiguous  individuals  always  pass 
along  in  the  same  direction,  or  whether  their  move- 
ments appear  independent  of  each  other.     In  the  latter 


SIMPLICITY   OF   THE   LOAVEST   ORGANISMS.  5 

ease  it  is  impossible  to  suppose  that  they  are  only  hur- 
ried along  by  currents,  and  it  is  safe  to  conclude  that 
even  these  simplest  organisms  are  gifted  with  the 
power  of  independent  motion.  Of  the  nature  of  this 
power  nothing  is  very  certainly  known.  The  organisms 
of  which  we  are  speaking  belong  to  the  lowest  rank  of 
the  organic  world.  They  are  living  beings,  for  they 
move,  they  grow,  and  they  multiply ;  they  can  be 
killed,  for  instance,  by  boiling  water,  and  their  inde- 
pendent motion  then  ceases.  This  is  nearly  all  that  is 
kno\Mi  of  them.  Next  to  them  rank  organisms  which 
are  somewhat  more  complex  in  structure.  They  are 
small  lumps  of  semi-fluid,  granular  matter,  which  is 
called  protojjlasm^  This  semi-fluid  condition — inter- 
mediate between  a  liquid  and  a  solid  state — is  charac- 
teristic of  all  organic  matter.  It  is  due  to  the  absorp- 
tion of  water  into  the  pores  of  a  solid  mass,  which  in 
consequence  swells  and  undergoes  an  intimate  mixture 
with  the  water,  and  in  which  the  molecules  can  then 
change  their  positions  in  the  same  way,  though  perhaps 
not  quite  so  easily,  as  otherwise  is  possible  only  in  liquids. 
A  thin  jelly-like  clay  would  afford  the  best  representa- 
tion of  this  condition  of  aggregation  of  protoplasm. 
A  small  lump  of  protoplasm  of  this  sort  may  in  itself 
represent  an  independent  living  being,  exhibiting  vital 
phenomena  of  such  a  kind  that  it  is  impossible  to  refuse 
to. call  it  an  'animal.'  It  moves  by  its  own  force,  and, 
as  it  would  seem,  voluntarily  ;  it  imbibes  matter  for  its 
own  nutrition  from  the  sm-rounding  liquid  ;  it  grows,  it 
multiplies  its  kind,  and  it  dies.     The  most  evident  mo- 

'  Sometimes,  but  not  always,  in  addition  to  these  fine  granules,  a 
larger,  bladder-like  bodj^  called  the  kernel  or  nucleus,  is  seen  within 
the  mass. 


b  PHYSIOLOGY    OF    MUSCLES   AND    NERVES. 

tion  in  this  case  occurs  in  two  ways.  Sometimes  single 
processes  are  seen  to  protrude  from  the  whole  mass; 
these  processes  gradually  affect  the  whole  granular 
mass,  so  that  the  whole  body  is  displaced,  and  a  genuine 
change  of  position  happens  to  the  animal ;  or  the  pro- 
cesses being  again  retracted,  other  similar  processes  are 
protruded  from  another  part  of  the  body,  in  such  a  way 
that  the  direction  of  motion  is  changed ;  in  short,  the 
animal  creeps  about  on  the  glass  plate  on  which  it  is  ob- 
served by  means  of  these  processes.  Meanwhile  currents 
of  granules  can  be  seen  within  the  mass ;  closer  obser- 
vation, however,  shows  that  the  motion  in  this  case  is 
only  passive,  and  that  it  is  the  result  of  a  continuous 
wave-like  displacement  of  the  protoplasm. 


1   ,  ^'      / 


^      y'  /^       f^.        H        N 


Fig.  1.     A.-Ma:i5.E. 

a.  Amoeba  verrucosa,    h.  Amceba  poiTecta, 

5.  Movements  entirely  similar    to   those  in  these 
independent  living  animals,  called  Amoebai^   occur  in 


PROTOPLASMIC    AND    AMCEBOID    MOVEMENTS.  7 

more  highly  organised  beings,  vegetable  as  well  as  ani- 
mal. All  living  beings  are  fundamentally  composed  of 
just  such  lumps  of  protoplasm  as  we  see  in  the  AmoehcB. 
jNIost  of  these  lumps  of  protoplasm  have,  however, 
essentially  changed  their  appearance,  and,  at  the  same 
time,  their  qualities,  so  that  it  is  only  from  the  evolu- 
tion of  the  parts  that  we  know  them  to  have  originated 
from  such  lumps.  Moreover,  even  in  developed  organ- 
isms separate  parts  always  occur  which  are  in  all  re- 
spects similar  to  such  lumps  of  protoplasm  as  the 
Amoehce,  and  which  move  like  the  latter.  It  is  a  well- 
known  fact,  that  Avhen  a  drop  of  blood  is  placed  under 


Fjg.  2.    White  blood-corpusclf.s  fro.m  a  guixea-pig. 

a,  b,  c.  Various  forms  assumed  by  one  and  the  same  corpuscle. 

the  microscope,  a  very  large  number  of  small  red  bodies, 
•to  which  the  red  colour  of  the  blood  is  due,  are  seen 
within  it.  And  scattered  about  among  these  red  blood- 
corpuscles  are  seen  colourless  or  white  blood-corpuscles, 
round  or  jagged  in  form,  and  containing  granidar  pro- 
toplasm with  a  kernel  or  nucleus.  If  the  blood  has 
been  j)laced  on  a  warmed  glass,  and  if  it  is  observed 
at  a  temperature  of  from  35  to  40  degrees  C,  these 
blood-corpuscles  exhibit  active  movements  entirely 
similar  to  those  of  the  Amabce,  and  which  have,  there- 
fore, been  called  Amoeboid  movements.  The  corpuscles 
send  out  processes  and  again  retract  them ;  they  creep 
about  on  the  glass ;  and,  in   short,  they  behave  exactly 


8  PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 

like  ATYioebcG,  and  like  the  latter  they  even  absorb  matter, 
such  as  granules  of  any  colouring  substance  which  may 
have  been  added,  from  the  blood-fluid — they  eat,  that 
is — and  after  a  time  they  again  reject  this  matter. 
Moreover,  the  other  form  of  motion  described  above, 
the  protoplasmic  movements  or  granule  currents,  may 
also  be  seen  in  parts  of  compound  organisms.  If  the 
tiny  hairs  of  the  stinging  nettle  are  placed  under  the 
microscope,  it  appears  that  each  hair  consists  of  a  closed 
sac  or  pouch,  over  the  inner  surface  of  which  protoplasm 
is  spread  in  a  thin  layer.  Even  this  represents  a  much 
more  advanced  modification  of  the  protoplasmic  mass,  but 
yet  the  protoplasm  still  retains  its  power-  of  indepen- 
dent motion.  Wave-like  movements  are  seen  to  pass 
over  the  mass  of  the  protoplasm,  and  by  this,  just  as  in 
the  Amoehce,  a  current  is  apparently  produced  among 
the  granules.  For  a  time  the  movement  continues 
in  one  direction  ;  then  it  suddenly  ceases  and  begins 
again  in  an  opposite  direction ;  sometimes  one  cur- 
rent separates  itself  into  two,  others  unite,  and  so  on. 
If  the  protoplasm  dieS: — and  this  may  be  artificially 
caused  by  the  application  of  heat — all  motion  ceases. 
It  is  inseparably  bound  up  with  the  vital  powers  of  the 
cells. 

6.  The  free  protoplasmic  mass,  as  seen  in  the 
Amoeha,  is  one  of  the  simplest  of  organic  forms.  Such 
masses  sometimes  occur  in  groups,  which  thus  repre- 
sent colonies  of  organisms,  each  of  the  components 
of  which,  however,  retains  complete  independence, 
and  is  exactly  like  every  other.  Sometimes,  however, 
modification  takes  place  amongst  these ;  and  when 
these  modifications  advance  at  an  unequal  rate  in 
the  separate  members  of  the  colony,  a  composite  or- 


ELEMENTARY  ORGANISMS ;   DIFFERENTIATION  OF  TISSUES.  \) 

ganism  with  variously  formed  parts  is  the  result.  Each 
part  is  originally  a  completely  independent  organism  of 
equal  value  with  all  the  others,  and  each  has,  therefore, 
been  very  aptly  called  an  elementary  organism.  But 
together  with  the  modification  in  the  form,  a  change 
usually  takes  place  in  the  qualities.  Of  the  various 
qualities  possessed  by  the  protoplasm  in  its  original 
form,  some  are  lost,  others  are  especially  developed. 
A  colony  of  uniform  elementary  organisms  may  be 
likened  to  a  society  in  the  lowest  stage  of  civilisation, 
in  which  each  member  still  personally  performs  all  the 
tasks  necessary  to  life  ;  but  a  composite  organism,  with 
variously  developed  and  modified  elementary  organisms, 
may  be  likened  to  a  modern  state  of  which  the  various 
members  perform  very  different  tasks.  The  more  highly 
developed  plants  and  animals  are  of  this  sort.  They 
originate  from  a  number  of  elementary  organisms — or 
cells,  as  they  are  also  called — originally  uniform;  but 
these  develop  in  very  different  ways — differentiate,  as 
is  technically  said,  and  then  acqmre  very  different  ap- 
pearance and  purpose.  In  some  the  power  of  causing 
motion,  which  is  originally  common  to  all  protoplasm, 
is  especially  developed ;  others  effect  sensation,  which 
power  was  possibly  or  probably  present  even  in  the 
simple  protoplasm.  These  will  be  fully  discussed  in  the 
following  chapters.  But  before  doing  this,  a  few  words 
must  be  said  as  to  one  form  of  these  modified  cells,  in 
which  the  power  of  generating  motion  is  already  de- 
veloped in  a  very  noticeable  degree,  and  serves  partly 
for  the  independent  movement  of  the  cell-body,  or  of 
the  animal  of  which  the  cell  is  a  part;  partly,  when 
occurring  in  fixed  bodies,  to  move  foreign  matter — that 
is,  for  the  drawing  in  of  food. 


10  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

7.  If  a  light  powder — such,  for  instance,  as  finely 
powdered  charcoal — is  spread  over  the  skin  of  the 
palate  of  a  living  or  a  recently  killed  frog,  the  powder 
is  seen  to  advance  with  some  speed  towards  the  gullet. 
Microscopic  examination  shows  that  this  skin  is  studded 
with  a  dense  layer  of  cylindrical  cells  standing,  palisade- 
like, side  by  side.  The  free  surface  of  each  of  these 
cells  is  studded  with  a  large  number  of  delicate  hairs 


Fig.  3. 
a.  Ciliated  cells,  pointed  be-  6.  A  single  ciliated  cell,  more 

low,  and,  with  other  cells,  enlarged    and    of    some- 

attached    to    the    mem-  what  more  modified  form, 

braue. 

or  ciliag,  which  are  in  continual  motion  in  a  definite 
direction  in  such  a  way  that  they  propel  all  such  liquid, 
together  with  the  particles  contained  in  this,  as  adheres 
to  their  upper  surface  in  that  direction.  This  is  called 
ciliary  motion.  It  occurs  very  frequently  in  the  animal 
body,  e.g.  in  the  windpipe  and  its  branches,  where  the 
motion  is  upward,  serving  to  propel  the  phlegm  to  the 
larynx,  from  which  it  can  be  thrown  out  by  coughing. 


CILIAEY   MOVEMENT.  11 

lu  many  fixed  animals  of  low  order  a  crown  of  cilise 
encircles  the  moutli-opening,  producing  a  current 
which  brings  water,  together  with  particles  floating  in 
the  latter,  to  the  animal  as  food.  Other  aquatic  ani- 
mals have  the  whole  or  a  part  of  their  upper  surface 
studded  with  cilise,  by  means  of  which  they  rotate  in 
the  water.  Finally,  there  are  bodies  which,  instead  of 
the  delicate  ciliate  hairs,  possess  only  a  larger  and 
stronger  whip-like  process  by  the  sinuous  motions  of 
which  these  animals  move  themselves  about  in  the 
water,  as  a  boat  may  be  moved  by  the  quick  motion  of 
the  rudder,  or  as  a  water-newt  propels  itself  by  the 
sinuous  motion  of  its  tail. 

None  of  these  motions  are,  however,  equal  in  force 
and  etfectiveness  to  those  which  are  produced  by  muscles. 
In  higher  animals,  muscles  occur  in  two  forms, — either 
as  smooth  muscle-fibres,  or  as  striated  muscle-fibres.  The 
former  are  spindle-shaped  cells  which  have  grown  out 
in  a  longitudinal  direction,  and  which  have  rod-shaped 
kernels  (nuclei)  and  pointed  ends,  sometimes  twisted 
like  a  corkscrew.  The  latter  are  produced  by  the  coa- 
lescence and  amalgamation  of  several  cells,  the  contents 
of  which  have  undergone  an  important  change.  These, 
and  the  qualities  of  these,  will  be  fully  discussed  in 
the  following  chapters. 


12  .PHYSIOLOGY    OF   MUSCLES   AND    NEKVES. 


CHAPTER  II. 

1.  Muscles,  Iheir  form  and  structure;  2.  Minute  structure  of 
striated  muscle-iibres  ;  3.  Connection  of  muscles  and  bones ; 
4.  Bones  and  bone-sockets ;  5.  The  law  of  elasticity ;  6.  Elas- 
ticity of  the  muscles. 

1.  Muscles  are  elastic  structures  capable  of  altering 
their  form — that  is,  of  becoming  shorter  and  thicker. 
In  the  bodies  of  the  more  highly  developed  animals 
they  constitute  those  masses  which  are  commonly  called 
flesh.  The  flesh,  when  carefully  studied,  is  found  to 
consist  of  bundles  of  fibres,  the  ends  of  which  are  pro- 
duced into  white  cords,  most  of  which  are  attached  to 
bones.  When  one  of  these  muscles  shortens,  it  exerts 
a  strain,  by  means  of  these  white  cords,  on  the  bones ; 
and  these  latter,  being  movable  the  one  against  the 
other,  are  thus  put  in  motion  by  the  shortening  of  the 
muscle.  All  muscles  are  not,  however,  arranged  in  this 
way ;  some  ring-shaped  muscles  form  the  walls  of  sacs 
or  pouches,  and  these,  by  contracting,  decrease  the 
space  within  these  cavities,  so  that  the  contents  of  the 
latter  are  thus  forced  onward.  In  any  case,  muscles 
always  serve  to  produce  movement — either  of  the  limbs 
in  opposition  to  each  other,  or  of  the  whole  animal,  or 
of  the  substances  contained  within  the  cavities. 

We  must  first  confine  our  attention  to  those  muscles 
which  are  attached  to  bones,  and  which  are  therefore 


FORM   A^D   STRUCTURE    OF   MUSCLES.  13 

called  skeleton  muscles.  These  muscles  occm-  in  various 
forms.  Sometimes  they  are  flat,  thin  bands,  and  some- 
times cylindrical  cords,  some  of  which  are  of  considerable 
length.  Others  again  are  thicker  in  the  middle  than  at 
the  ends  ;  in  these  cases  the  middle  is  called  the  trunk, 
the  ends  are  spoken  of  as  the  head  and  tail,  of  the  muscle. 
Some  muscles  have  two  or  more  heads — that  is,  two  or 
more  ends — springing  from  different  points  on  the  bone, 


03333301303 


Fig.  4.     Stuiatku  jirsrLh-FiBnrs. 
a.  Two  fibres  cat  tlirouph  in  the  middle,  and  passing,  on  the  left,  into  tendons.    6.  A 
single  muscle-fibre  deprivetl  of  its  discs,  and  separating  into  fibrillas.     c.  Two 
single  fihrilliC.    rf.  A  muscle-fibre  separating  into  its  discs. 

and  uniting  in  a  common  trunk.  But  the.?e  muscles, 
whatever  their  external  shape,  always  consist  of  several 
fibres,  united  into  a  bundle,  and  together  forming  the 
muscle  as  a  whole.  One  of  these  fibres,  when  isolated, 
will  be  found  to  be  very  minute,  and  scarcely  visible  to 
the  naked  eye ;  when  seen,  enlarged  from  250  to  300 
times,  under  the  microscope,  it  appears  as  a  pouch, 
consisting  of  a  firm,  solid  wall,  with  certain  contents ; 
and  this  contained  matter  exhibits  alternate  licfhter  and 


14  PHYSIOLOGY    OF   MUSCLES   AND    NEKVES. 

darker  streaks,  placed  at  right  angles  to  the  longitudinal 
direction  of  the  fibres.  For  this  reason,  these  muscle- 
fibres  are  called  streaked  or  striated  muscles,  in  order 
to  distinguish  them  from  certain  others  of  which  we 
shall  presently  learn.  In  order  to  obtain  an  approxi- 
mate idea  of  the  appearance  of  one  of  these  fibres,  we 
may  imagine  it  as  a  roll  of  coins,  the  separate  pieces  of 
which  are,  however,  transparent  and  alternately  lighter 
and  darker.  Some  observers  have  indeed  assumed  that 
a  muscle-fibre  really  consists  of  discs  of  this  sort,  ranged 
side  by  side.  The  fibres,  when  treated  with  certain 
chemical  re-agents,  separate  into  these  discs,  and  while 
some  of  them  yet  remain  attached  to  each  other,  the 
fibre  very  closely  resembles  a  roll  of  coins  the  pieces  of 
which  are  falling  away  from  each  other.  But  there  are 
other  re-agftnts  which  split  up  the  fibre  in  a  longitudinal 
direction,  so  that  it  separates  into  extremely  delicate 
smaller  yi6?'es  or  fihrillcs  each  of  which  still  exhibits  the 
alternation  of  lighter  and  darker  parts,  which,  in  the 
entire  fibre,  produce  the  transverse  striation.  More- 
over it  can  be  shown  that  a  muscle-fibre  when  recently 
taken  from  the  living  animal  must,  in  reality,  be  of  a 
fluid,  or,  at  least,  of  a  semi-fluid  nature.  So  that  it  is 
impossible  to  affirm  that  either  the  discoid  or  the  fibril- 
loid  structm'e  actually  exist  in  the  muscle-fibre  itself ; 
it  must  rather  be  assumed  that  both  forms  of  structure 
are  really  the  result  of  the  application  of  re-agents 
which  solidify  the  originally  fluid  mass  and  split  it  up 
in  a  longitudinal  or  transverse  direction. 

2.  It  is  hard  to  say  what  the  true  character  of  the 
fresh,  or,  as  we  may  also  call  it,  the  living  muscle-fibre 
really  is.  Eecent  observations  by  means  of  very  much 
improved  and  very  highly-magnifying  microscopes,  have 


MINUTE  STRUCTURE   OF  STRIATED    MUSCLE-FIBRES.    15 

broucfht  to  lig-ht  other  differences  besides  that  of  the 
niere  alternation  of  lighter  and  darker  streaks.  Of 
the  highest  importance  as  explaining  the  structure  of 
muscle-fibres  are  the  researches  of  E.  von  Briicke  into 
the  phenomena  exhibited  by  muscle-fibres  in  polarised 
light.  According  to  modern  physical  views,  light  de- 
pends on  the  vibrations  of  ether,  an  impalpable  matter 
spread  throughout  the  universe  and  present  in  aU  bo- 
dies. These  vibrations  always  proceed  at  right  angles 
to  the  direction  in  which  motion  is  propagated.  With- 
in this  imaginary  plane  at  right  angles  to  the  ray  of 
light,  an  ether  particle  may  vibrate  in  the  most  diverse 
directions.  Under  certain  circumstances,  however,  they 
all  vibrate  in  one  and  the  same  plane,  in  which  case 
the  ray  exhibits  certain  peculiarities,  and  is  said  to  be 
polarised.'  Certain  crystals  have  the  power  of  polaris- 
ing such  rays  of  light  as  pass  through  them.  A  few, 
at  the  same  time,  separate  each  ray  of  Kght  into  two 
rays  which  move  separately  from  the  original  ray. 
Such  crystals  are  called  double-refracting  bodies.  Ice- 
land spar  or,  as  it  is  also  called,  double  spar,  is  the  best- 
known  example  of  such  a  double-refracting  body. 
Briicke  has  shown  that  of  the  two  substances  whicih 
form  the  alternate  layers  of  striated  muscle,  the  one 
transmits  light  unchanged,  the  other  is  possessed  of 
double-refracting  powers.  But,  as  has  already  been 
said,  the  contents  of  a  living  muscle-fibre  must  be  re- 
garded not  as  solid  but  rather  as  fluid,  or  at  least  as 
semi-fluid;  and  observations  made  on  living  muscle- 
fibres  show  that  the  streaks  are  not  incapable  of  modi- 
fication in  their  breadth   and  in  their  distance  from 

'  This  circumstance  is  treated  in  more  detail  in  Lommel's  Tlie 
Nature  of  Ligltt  (International  Scientitic  Series,  Vol.  XVIII.) 


16      PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

each  other.  Briicke,  therefore,  supposes  that  the  muscle 
substance  is  in  itself  homogeneous  or  uniform,  but  that 
in  it  are  inserted  small  particles  which  are  of  double- 
refracting  power.  When  these  particles  are  massed  in 
large  numbers,  and  are  regularly  arranged,  they  refract 
the  light  doubly,  so  that  the  whole  of  that  particular 
part  seems  to  refract  doubly,  while  the  intermediate 
parts,  since  they  contain  few  or  none  of  the  particles 
in  question,  continue  to  refract  simply.  These  latter 
parts,  however,  when  seen  under  ordinary  unpolarised 
light,  so  that  it  is  impossible  to  judge  of  their  powers 
of  double  refraction,  appear  lighter,  while  the  former 
appear  darker ;  and  so  together  they  cause  the  striated 
appearance  of  the  muscle. 

3.  In  one  of  these  muscle-fibres  it  is  necessary  to 
distinguish  the  contained  matter  and  the  containing 
pouch.  The  latter  is  called  the  muscle-fibre  pouch,  or 
sarcolemTiia.  In  it,  especially  after  the  addition  of 
acetic  acid,  which  causes  the  whole  fibre  to  swell  and 
become  more  transparent,  a  number  of  longish  pointed 
kernels  {nuclei)  are  seen,  and  similar  kernels  occur  also 
in  parts  within  the  muscle-fibre.  To  the  ends  of  the 
muscle-fibre,  which  are  rounded  and  are  very  uniformly 
enclosed  by  the  pouch,  which  must  therefore  be  re- 
garded as  a  long  closed  sac,  the  white  cords  mentioned 
above  attach  themselves,  and  these  are  completely 
ooalescent  with  the  sarcolemma. 

They  consist  of  strong  slender  threads  of  the  natru-e 
of  the  so-called  connective  tissue.  As  a  considerable 
number  of  muscle-fibres  constitute  the  trunk  of  the 
muscle,  these  threads  also  unite  into  cords  which  are 
called  the  muscle-tendons.  They  are  sometimes  short, 
sometimes  long,  thicker  or  thinner  according  to  the 


CONNECTION    OF   MUSCLES   AND   BONES. 


17 


size  of  tHe  muscle,  and  they  serve  to  attach  the  muscles 
firmly  to  the  bones,  to  which,  acting  like  ropes,  they 
transmit  the  tension  of  the  muscles.  One  of  the  two 
bpnes  to  which  a  muscle  is  attached  is  usually  less 
mobile  than  the  other,  so  that 
when  the  muscle  shortens, 
the  latter  is  drawn  down 
against  the  former.  In  such 
a  case  the  point  of  attach- 
ment of  the  muscle  to  the 
less  mobile  bone  is  called  its 
origin,  while  the  point  to 
which  it  is  fixed  on  the  more 
mobile  bone  is  called  its  at- 
tachment {epiphysis).  For 
instance,  there  is  a  muscle 
which,  originating  from  the 
shoulder-blade  and  collar- 
bone, is  attached  to  the 
upper  arm-bone ;  when  this 
muscle  is  shortened,  the  arm 
is  raised  from  its  perpen- 
dicular pendant  position  in- 
to a  horizontal  position.  A 
muscle  is  not  always  ex- 
tended between  two  con- 
tiguous bones.  Occasionally 
passing  over  one  bone,  it  at- 
taches itself  to  the  next.  This  is  the  case  with  several 
muscles  which,  originating  from  the  pelvic  bone,  pass 
across  the  upper  thigh-bone,  and  attach  themselves  to 
the  lower  thigh-bone.  In  such  cases  the  muscle  is 
capable   of  two  different    movements:    it   can    either 


Img. 


CALF  MUSCLIi 
miiis),  WITH 
DONS. 


The     DOUBt.E-nKADED 

(3/.    gastiocne- 

ITS      TWO     TEN- 


a.  The  two  liea'ls.  c.  Tlie  com- 
m?ncement  of  the  tendon  which  at 
k  is  attached  to  the  heel-bone. 


18  PHYSIOLOGY   OF    MDSCLES    AND    NP^KVES. 

stretch  the  knee,  previously  bent,  so  that  the  upper 
and  the  lower  thigh-bones  are  in  a  straight  line  ;  or  it 
can  raise  the  whole  extended  leg  yet  higher  and  bring 
it  nearer  to  the  pelvis.  But  the  points  of  origin  and 
of  attachment  of  muscles  may  exchange  offices.  When 
both  legs  stand  firmly  on  the  ground,  the  above-men- 
tioned muscles  are  unable  to  raise  the  thigh  ;  instead, 
on  shortening,  they  draw  down  the  pelvis,  which  now 
presents  the  more  mobile  point,  and  thus  bend  forward 
the  whole  upper  part  of  the  body.  In  order,  therefore, 
to  understand  the  action  of  the  skeleton,  the  separate 
bones  of  the  skeleton  and  their  connection  must  first  be 
studied. 

4.  All  bones  are  classified  according  as  they  are 
flat,  short,  or  long.  Flat  bones,  as  their  name  indicates, 
are  expanded  chiefly  in  two  directions  ;  they  form  thin 
plates.  Short  bones  are  expanded  almost  equally  and 
but  slightly  in  all  three  directions.  In  long  bones, 
finally,  the  expansion  in  the  longitudinal  direction  con- 
siderably exceeds  that  in  the  other  two  directions.  The 
extremities,  the  arms  and  legs,  are  chiefly  formed  of 
these  long  bones.  The  arm,  for  instance,  consists  of 
the  long  bone  of  the  upper  arm,  to  which  are  attached, 
first,  two  other  long  bones  (called  the  elbow  bone  and 
the  radius),  which  together  form  the  fore-arm;  and 
secondly,  by  means  of  several  shorter  bones,  which  con- 
stitute the  wrist,  the  hand  itself;  this  latter  consists  of 
the  five  bones  of  the  palm  and  the  five  fingers,  of  which 
the  first  has  two,  the  others  each  have  three  divisions. 
In  all  these  bones,  with  the  exception  of  those  of  the 
wrist,  a  long  middle  part,  or  shaft,  with  two  thickened 
ends,  are  noticeable.  As  this  shaft  is  hollow,  these 
bones  are  also  spoken  of  as  cylindrical.     The  expanded 


BONES  AND  THEIR  SOCKETS. 


19 


ends  are  rounded  and  are  provided  with  a  smooth  car- 
tilaginous covering.  The  smooth  ends  of  two  contiguous 
bones  fit  into  each  other,  so  that  when  the  surfaces  of 
the  two  ends  glide  the  one  over  the  other,  the  two 
bones  are  capable  of  motion 
in  opposite  directions.  The 
point  of  attachment  between 
two  bones  is  called  the  socket ; 
and  the  surfaces  of  the  two 
ends  of  the  bones  where  they 
touch  each  other  are  called  the 
socket  surfaces.  The  motion 
which  these  bones  have  the 
power  of  exercising  in  opposite 
directions  varies  with  the  form 
of  these  socket  surfaces.  When 
the  surface  of  the  socket  is  of 
semi-spherical  form,  the  motion 
is  most  free,  and  can  be  exert- 
ed backward  or  forward  in  any 
direction.  The  socket  in  this 
case  is  called  a  ball-  or  nut- 
socket.  An  example  of  this  sort 
may  be  seen  at  the  upper  end 
of  the  bone  of  the  upper  arm.  Fig.  g.  The  boxes  of  the 
where  it  ends  in  a  ball-shaped  '^^'^'' 

surface  which   is  applied   to   a  "  ???o"  le"  7^™- 4: 
corresponding  socket  surface  in       SlYoXrottr eibow.°"" ''*. 
the  shoulder  blade.      In  other 

cases  motion  can  only  take  place  in  a  definite  direc- 
tion, as,  for  instance,  in  the  case  of  the  socket  con- 
necting the  upper  and  fore  arms.  These  are  called 
hinge-sockets.     They  serve  to  increase  or  decrease  the 


20  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

angle  between  the  two  parts.  To  mention  all  the 
various  forms  of  sockets  and  the  movements  which  they 
allow  would  lead  us  too  far;  it  is  sufficient  to  have 
shown  that  the  action  of  the  muscles  is  affected  by  the 
bones  between  which  they  are  extended.  In  order,  how- 
ever, to  examine  the  contractile  power  of  muscles,  the 
latter  may  be  detached  from  the  bones  and  examined 
by  themselves. 

The  muscles  of  warm-blooded  animals  are  but  ill- 
adapted  for  this  purpose  ;  fortunately,  however,  those  of 
cold-blooded  animals  not  only  possess  the  same  qualities, 
but  retain  the  power  of  contraction  long  after  their  re- 
moval from  the  animal,  a  circumstance  which  renders 
them  very  valuable  for  purposes  of  study.  The  frog  is 
most  frequently  used  in  such  experiments,  both  on 
account  of  its  common  occurrence  and  of  the  power  of 
its  muscles.  If  a  frog  is  beheaded  and  an  entire  muscle 
is  cut  from  either  its  upper  or  lower  thigh,  one  of  the 
tendons  of  this  muscle  may  be  fixed  in  a  vice,  and 
its  other  tendon  may  be  connected  with  a  lever,  re- 
presenting as  it  were  the  bone,  by  the  motion  of  which 
the  contraction  of  the  muscle  may  be  studied.'  Weights 
may  also  be  attached  to  this  lever  in  such  a  way  that 
the  burden  which  the  muscle  is  capable  of  lifting  may 
be  studied.  It  will  at  once  be  observed  that  the  muscle 
is  extended  when  such  weights  are  attached,  and  is 
extended  more  in  proportion  as  the  weight  attached 
is  heavier.  This  results  from  the  elastic  qualities  of 
muscle ;  and  before  examining  the  contraction  of  muscles 
it  will  be  necessary  carefully  to  study  their  elasticity. 

1  In  order  to  fasten  the  mnscle  more  securely,  it  is  generally 
well  to  leave  a  small  piece  of  the  bone  at  either  end  attached  to  the 
tendons,  and  to  fasten  the  muscle  by  these. 


LAW   OF   ELASTICITY.  21 

5.  Those  bodies  wliicli  alter  their  form  under  the 
influence  of  external  forces,  and  resume  their  original 
form  on  the  cessation  of  these  external  forces,  are  called 
elastic.  The  greater  these  alterations  are,  the  greater 
is  the  elasticity  of  the  body.  The  external  force  pro- 
ducing the  alterations  may  be  either  tension,  extending 
the  body  in  one  particular  direction ;  or  it  may  be  pres- 
sure, compressing  the  body  into  a  smaller  space ;  or, 
again,  it  may  be  tension  combined  with  pressure,  bend- 
ing the  body.  We  are  only  concerned  with  the  force 
of  tension,  which  acting  on  the  body  in  a  longitudinal 
direction  extends  it ;  that  is  to  say,  we  are  about  to 
study  the  elasticity  of  muscle  tension.  Physicists 
have  experimented  on  elastic  tension  in  bodies  of  the 
most  diverse  kinds.  But  bodies  of  regular  shape,  rods 
or  threads,  the  length  of  which  considerably  exceeds 
the  thickness,  are  best  adapted  for  such  experiments. 

On  firmly  fastening  a  body  of  this  kind,  for  instance 
a  steel  wire  or  a  glass  thread,  to  a  beam  in  the  ceiling, 
and,  after  accurately  measuring  its  length,  attaching 
weights  to  the  lower  end,  it  will  be  found  that  the  ex- 
tension caused  by  these  weights  is  greater  in  the  first 
place  in  proportion  as  the  weights  causing  the  extension 
are  greater,  and  in  the  second  place  in  proportion  as  the 
body  which  is  extended  is  longer.  And,  on  the  con- 
trary, with  any  given  weight  and  length,  the  extension 
will  be  found  to  be  less  in  proportion  as  the  body  is 
thicker,  or,  in  other  words,  the  larger  is  its  cross-section. 
This  latter  circumstance  may  be  easily  understood  by 
assmning  that  the  rod  or  thread  consists  of  a  number 
of  smaller  rodlets  or  tiny  threads  which  lie  evenly  side  by 
side.  If,  for  instance,  we  select  for  this  experiment  a 
steel  rod,  the   cross-section  of  which  measures  exactly 


22  PHYSIOLOGY    OF   MUSCLES   AND   NEKVES. 

one  square  centimetre,  we  may  assume  that  this  con- 
sists of  a  hundred  rodlets  of  equal  length,  lying  side  by 
side,  the  cross-section  of  each  of  which  measures  ex- 
actly one  square  millimetre.  On  attaching  a  weight  of 
one  kilogramme  (  =  1000  gr.)  to  this  rod,  each  one  of  the 
hundred  thin  rodlets  would  have  to  bear  a  weight  of 
but  ten  grammes.  Comparing  with  this  the  tension  of 
another  steel  rod  of  the  same  length,  but  of  which  the 
cross-section  measures  twice  as  much,  we  may  assume 
that  this  second  rod  is  composed  of  two  hundred  minute 
rodlets,  the  cross-section  of  each  of  which  measures  one 
millimet.re.  The  weight  being  now  distributed  between 
two  hundred  of  these  rodlets,  each  has  to  support  a 
weight  of  only  five  grammes.  This  explains  why  the 
tension  by  the  same  weight  is  only  half  as  great  in  a 
rod  of  double  thickness.  That  the  extension  is  pro- 
portionate to  the  length  of  the  extended  rod  can  be 
explained  in  the  following  way.  According  to  the  views 
of  modern  physicists  every  body  consists  of  a  number 
of  small  molecules  or  particles  which  are  held  at  definite 
distances  from  each  other  by  attractive  and  repulsive 
forces.  On  fastening  a  rod  by  its  upper  end  and  at- 
taching a  weight  to  its  lower  end,  the  molecules  are 
by  these  means  slightly  separated  from  each  other. 
The  sum  of  all  these  small  separations  represents  that 
whole  extension  measurable  at  the  end.  The  longer 
any  given  body  is,  the  greater  is  the  number  of  these 
small  particles  which  occur  in  its  whole  length,  and 
consequently  the  greater  must  its  extension  be,  pro- 
vided all  other  circumstances  are  equal. 

From  these  observations  may  be  deduced  a  law  as 
to  elastic  tension,  which  is  further  confirmed  by  accurate 
researches,  and  this  law  is  that  the  tension  is  directly 


ELASTICITY   OF   MUSCLES.  23 

'proportionate  to  the  length  of  the  body  extended,  and 
to  the  amount  of  the  extending  iveights ;  and  that  it 
is  also  proportionate  in  inverse  ratio  to  the  diameter 
of  the  extended  body.  This  is  called  the  law  of  elas- 
ticity, of  Hook  and  S'Grravesande.  In  order,  however, 
to  find  the  tension  of  a  particular  body,  another  factor 
connected  with  the  nature  of  the  body  itself  must  be 
known  ;  for,  under  otherwise  equal  conditions,  the  ten- 
sion, for  instance,  of  steel,  as  found  by  actual  experiment, 
differs  from  that  of  glass,  and  that  of  the  latter  from 
that  of  lead,  and  so  on.  In  order,  therefore,  to  be  able 
to  calculate  the  tension  in  the  case  of  all  bodies,  the 
tension,  experimentally  found,  must  be  reduced  to  the 
units  of  length  and  diameter  of  the  weighted  bodies, 
and  to  units  of  the  weight  applied.  This  gives  a  figure 
which  expresses  the  tension  of  a  body  of  a  given  nature 
of  one  milKmetre  in  length,  and  with  a  cross-section 
measuring  one  square  centimetre  when  supporting  a 
weight  of  one  kilogramme.  This  result,  which  is  con- 
stant in  the  case  of  every  substance,  whether  it  be  steel, 
glass,  or  aught  else,  is  the  co-efficient  of  elasticity  of 
that  substance. 

6.  Similar  researches  have  been  made  in  the  case 
of  organic  bodies  also,  such  as  caoutchouc,  silk,  muscle, 
&c.,  and  in  so  doing  certain  peculiarities  have  been 
observed  which  are  of  course  of  great  importance  to  us. 
In  the  first  place,  all  these  bodies- — which  we  may  also 
call  soft,  to  distinguish  them  from  those  rigid  bodies  of 
which,  up  to  the  present,  we  have  been  speaking — ex- 
hibit a  much  greater  extensibility.  That  is  to  say,  soft, 
organic  bodies  are  capable  of  far  greater  extension  than 
are  rigid,  inorganic  bodies  of  equal  length  and  diameter, 
and  under  the  application  of  equal  weight.      But  the 


24  PHYSIOLOGY    OF    MUSCLES    AND   NERVES. 

former  also  exhibit  another  pecuharity.  If  a  weight  is 
attached  to  a  steel  wire,  or  some  other  similar  body, 
the  latter  extends,  and  retains  its  new  length  so  long 
as  the  weight  acts  upon  it ;  but  as  soon  as  the  weight 
is  removed  the  steel  resumes  its  original  length.  It  is 
not  so  in  the  case  of  inorganic  bodies.  For  instance, 
if  a  weight  is  attached  to  a  caoutchouc  thread  it  will  be 
found  that  the  latter  is  immediately  extended  to  a 
certain  length ;  but  if  the  weight  is  not  removed,  it 
will  be  found  that  the  caoutchouc  thread  extends  yet 
more,  and  the  weight  continues  to  sink,  though,  indeed, 
but  slowly,  and,  as  time  goes  on,  with  ever  decreasing 
speed.  But  even  at  the  end  of  twenty-four  hours  a 
slight  additional  extension  of  the  thread  is  observable. 
If  the  weight  is  then  removed,  the  thread  immediately 
becomes  considerably  shorter,  but  does  not  entirely  re- 
vert to  its  original  length;  it  attains  the  latter  very 
gradually  and  in  the  course  of  many  hours.  This  phe- 
nomenon is  known  as  the  gradual  extension  of  organic 
bodies.  It  takes  place  in  very  considerable  degree  in 
muscle,  and  naturally  increases  the  difficulty  of  deter- 
mining the  extensibility  of  muscles,  in  that  the  mea- 
surements differ  according  to  the  moment  at  which  they 
are  read.  It  is  safest  to  take  into  consideration  only 
that  extension  which  occurs  instantaneously,  without 
regard  to  that  which  gradually  follows. 

Various  apparatus  have  been  produced  for  examina- 
tion of  muscular  extension.  The  latter  can  be  most 
accuratelj'  read  by  means  of  the  apparatus  invented  by 
du  Bois-Eeymond,  represented  in  fig.  7.  The  muscle 
is  firmly  fastened  to  a  fixed  bearer,  its  upper  tendon 
being  fixed  in  a  vice.  A  small,  finely  graduated  rod  is 
fastened  to  the  lower  tendon  by  means  of  a  small  hook. 


ELASTICITY    OF   MUSCLES. 


25 


Below  the  graduations  the  rod  branches  into  two 
arms,  which  again  re -unite  at  a  lower  pointy  and  within 
the  space  thus  formed  a  scale- 
plate  is  fixed  for  the  reception  i^pi 
of  the  weights  which  it  is  de-  ijH 
sired  to  apply.  Finally  the  rod 
ends  in  two  vertical  plates  of 
thin  talc  standing  at  right 
angles  to  each  other,  and  these 
are  immersed  in  a  vessel  filled 
with  oil,  so  that,  while  offering 
no  obstacle  to  the  upward  and 
downward  motion  of  the  ap- 
paratus, they  prevent  any  lateral 
movement.  In  order  to  deter- 
mine the  extension  of  the  muscle, 
the  graduated  rod  attached  to 
it  must  be  observed  through  a 
lens,  and  it  must  be  noted  which 
divisional  line  of  the  graduated 
rod  corresponds  with  a  thread 
stretched  horizontally  across  the 
lens ;  weights  must  then  be  ap- 
plied, and  the  increase  in  length, 
which  declares  itself  by  an  alter- 
ation in  the  relative  position 
of  the  graduated  rod  and  the 
thread,  must  be  obsen^ed.  Of 
course,  in  calculating  the  ex- 
tensibility from  the  figures  thus 
obtained,  the  weight  of  the  ap- 
paratus attached  to  the  muscle  must  be  taken 
consideration. 


Fig.  7.    Du  Bou-TJky.moxd's 

API'ARATLS  FOU  TIIK 

STUDY      OF      ELASTIC      EX- 
TENSION   IX   MLSCI.E. 


into 


26 


PHYSIOLOGY    OF    MUSCLES    AIS^D   NERVES. 


Experiments  in  muscular  elasticity  may  also  be  made 
with  the  apparatus  briefly  described  above,  by  measuring 
the  extensions  of  the  muscle  by  the  variations  of  a  lever 
attached  to  it.  The  easiest  way  to  do  this  is  by  fasten- 
ing an  indicating  apparatus  to  the  lever  in  such  a  way 


Fig.  S.     Suiple  myograph. 


that  it  traces  the  movements  of  the  lever  on  a  plate  of 
smoked  glass  placed  in  front  of  it.  This  apparatus  is 
called  a  myography  or  muscle- writer.  Fig.  8  represents 
it  in  the  simplified  form  adopted  by  Pfliiger.  The  body, 
the  elasticity  of  which  is  to  be  examined,  is  firmly  fixed 


ELASTICITY    OF    MUSCLES.  27 

in  the  vice  C,  and  is  connected  witli  tlie  lever  E  E,  the 
point  of  which  touches  the  plate  of  smoked  glass.  The 
^Yeight  of  the  lever  is  held  in  equipoise  by  the  balance 
11.  When  ■weights  are  placed  in  the  scale-pan  at  F,  the 
lever  moves  upward,  and  its  point  marks  a  straight  line 
which  afifords  opportunity  for  measuring  the  amount  of 
the  extension. 

But  in  whatever  way  examined,  muscle,  in  common 
with  all  other  soft  bodies,  exhibits  another  variation 
from  the  bearing  of  rigid  bodies.  We  have  seen  that 
in  steel  or  similar  bodies  the  extension  is  exactly  pro- 
portionate to  the  weight  applied ;  that  is  to  say,  if  a 
given  steel  wire  is  extended  one  millimetre  by  one 
kilogramme,  then  the  amount  of  extension  caused  by 
two  kilogrammes  is  two  millimetres,  that  by  three  kilo- 
grammes is  three  millimetres,  and  so  on.  It  is  not  so 
in  the  case  of  muscle  and  other  soft  bodies.  They  are 
comparatively  more  extensible  by  light  than  by  heavy 
bodies.  For  instance,  if  the  extension  of  a  muscle 
when  carrying  ten  grammes  is  five  millimetres,  when 
carrying  a  Aveight  of  twenty  grammes  it  is,  not  ten 
millimetres,  but  perhaps  only  eight;  when  carrying 
thirty  grammes  it  is  only  ten  millimetres,  and  so  on. 
The  extension,  therefore,  becomes  continually  less  as 
the  weight  increases,  and  finally  becomes  unnoticeable 
by  the  time  that  the  point  at  which  the  muscle  is  torn 
by  the  applied  weights  is  reached.  This  behaviour  is 
of  importance,  because  the  conditions  of  elasticity  play 
an  important  part  in  muscular  operations.  The  muscle 
on  contracting  is  capable  of  lifting  a  weight.  The  same 
weight,  however,  extends  the  muscle,  and  the  co-opera- 
tion of  the  two  forces — the  contractile  tendency  and 
the  elastic  extension — produces,  as  we  shall  find,  the 
final  operation  on  which  labour  dependrf. 


28  PHYSIOLOGY   OF   MUSCLES   AND    NERVES. 


CHAPTEE   III. 

1.  Irritability  of  muscle ;  2.  Contraction  and  tetanus ;  3.  Height 
of  elevation  and  performance  of  work  ;  4.  Internal  work  during 
tetanus;  5.  Generation  of  heat  and  muscle-tone  ;  6.  Alteration 
in  form  during  contraction. 

1.  If  a  muscle  is  cut  from  the  body  of  a  frog,  and 
is  fastened  into  the  myograph  just  described,  it  never 
shortens  spontaneously.  If  this  does  seem  to  happen,  it 
may  safely  be  assumed  that  some  accidental  and  un- 
perceived  external  cause  has  influenced  it.  A  muscle 
may,  however,  always  be  induced  to  shorten  by 
pinching  it  with  tweezers,  by  smearing  it  with  strong 
acid,  or  by  bringing  certain  other  external  influences, 
the  nature  of  which  we  shall  presently  learn,  to  bear 
upon  it.  Muscle,  therefore,  never  shortens  sponta- 
neously, but  it  can  always  be  induced  to  do  so.  This 
quality  of  muscle  enables  us  to  produce  the  state 
of  contraction  at  pleasure,  and  to  examine  accm-ately 
the  nature  and  method  of  the  conditions  which  give 
rise  to  it  and  the  phenomena  by  which  it  is  accom- 
panied. 

The  myograph  which,  by  means  of  the  indicator 
attached  to  it,  marks  the  contraction  of  the  muscle  on 
the  smoked  glass  plate,  and  at  the  same  time  afi'ords 
opportunity  for  measuring  the  extent  of  the  contraction, 
will  presently  prove  of  yet  greater  service.     But  for 


2a 


H 


30  THYSIOLOGY    OF    MUSCLES   AND   NERVES. 

our  present  purpose — which  is  to  discover  whether  or 
not  contraction  takes  place  under  certain  circumstances 
— it  is  hardly  adapted.  It  may,  therefore,  be  replaced 
by  another  apparatus,  arranged  by  du  Bois-E.eymond 
especially  for  experiments  during  lectures,  and  called  by 
him  the  inuscle-telegraph.  The  muscle  is  fixed  in  a 
vice ;  its  other  end  is  connected  by  a  hook  with  a 
thread  running  over  a  reel.  The  reel  supports  a  long 
indicating  hand  to  which  a  coloured  disc  is  attached. 
The  muscle  in  shortening  turns  the  wheel  and  lifts  the 
disc ;  and  this  is  easily  seen  even  from  a  considerable 
distance.  A  second  thread,  slung  over  the  reel,  sup- 
ports a  brass  vessel  which  may  be  filled  with  shot,  so  as 
to  apply  aiJy  desired  weight  to  the  muscle. 

The  influences  which  cause  the  contraction  of  the 
muscle,  such  as  pinching  or  smearing  with  acid,  are 
called  irritants,  and  the  muscle  is  said  to  be  irritable, 
because  contraction  can  be  induced  in  it  by  these  means. 
The  irritants  already  spoken  of  are  mechanical  and 
chemical ;  they  labour  under  a  disadvantage  in  that  the 
muscle,  at  least  at  the  point  touched,  is  destroyed,  or 
at  least  is  so  changed  that  it  is  no  longer  irritable. 
There  is,  however,  another  form  of  irritant  which  is 
free  from  this  disadvantage.  If  the  vice  which  holds 
the  upper  end  of  the  muscle  and  the  hook  to  which  the 
lower  end  is  attached  are  fastened  to  the  two  coatings 
of  a  charged  Kleistian  or  Leyden  jar,  the  charge  acts  at 
the  moment  at  which  the  connection  is  formed,  and 
an  electric  shock  traverses  the  muscle.  At  the  same 
instant  the  muscle  is  seen  to  contract,  and  the  disc 
passes  abruptly  upward.  In  order  to  repeat  the  experi- 
ment it  would  be  necessary  to  re-charge  the  Kleistian 
jar.     But   similar  electric    shocks   may  be  more  con- 


IREITABILITY    OF    MUSCLES  31 

venientlj  produced  by  means  of  so-called  induction. 
Let  us  take  two  coils  of  silk-covered  copper  wire  and 
attach  the  two  ends  of  one  of  these  to  a  muscle.  An 
electric  current  from  a  battery  must  now  be  passed 
through  the  other  coil  A.  The  two  coils  being  com- 
pletely isolated  from  each  other,  the  current  passing 
through  A  can  in  no  way  enter  into  B  or  into  the  muscle 
attached  to  B.  If,  however,  the  electric  current  in  A  is 
suddenly  interrupted,  an  electric  shock  immediately 
arises  in  B,  a  so-called  inductive  shock ;  and  this  passes 
through   and  irritates  the  muscle ;  that  is  to  say,  a 


Fig.  10.     IxDUCTiox  coil. 

The  coil  A  is  connected  with  the  battery  by  means  of  tlie  wires  x  and  y  ;  the  other 
coil,  B,  is  connected  with  the  muscle  by  means  of  wires  fixed  at  q  and  p, 

sudden  contraction  of  the  muscle  is  observable  at  the 
instant  of  the  opening  of  the  cm'rent  in  coil  A  ;  and 
this  suddenly  lifts  the  disc  attached  to  the  muscle. 
The  same  thing  occurs  when  the  current  in  the  coil  A 
is  again  closed ;  so  that  this  electric  irritant  affords  an 
easy  and  simple  means  of  causing  this  sudden  con- 
traction of  the  muscle  at  pleasure.  This  contraction 
may  be  called  a  pulsation;  and  it  will  be  perceived 
from  the  description  of  the  above  experiments  that  a 
simple  electric  shock,  such  as  is  afforded  by  the  dis- 
charge of  a  Kleistian  jar,  or  any  similar  inductive 
shock,  is  the  most  convenient  means  of  producing  such 
a  pulsation  as  often  as  it  is  required. 


32  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

An  electric  current  from  the  battery  itself  is  also 
capable  of  acting  as  an  irritant  on  muscle.  If  the  poles 
of  the  battery  are  connected  with  the  muscle,  a  constant 
current  passes  through  it.  If  one  of  the  connecting 
wires  consists  of  two  parts,  a  capsule  filled  with  quick- 
silver may  be  inserted  between  the  cut  ends.  One  end 
of  the  wire  must  be  allowed  to  remain  immersed  in  the 
quicksilver  ;  the  other  end  must  be  bent  into  the  form 
of  a  hook  so  as  to  allow  it  to  be  easily  immersed  in,  and 
again  withdrawn  from,  the  quicksilver.  This  makes 
it  easy  to  close  the  current  within  the  muscle,  and 
to  interrupt  it  again  at  pleasure.  At  the  moment 
at  which  the  current  is  closed,  a  pulsation  is  observed 
entirely  similar  to  that  which  would  be  produced  by 
an  electric  shock.  The  muscle  contracts,  and  the  disc 
is  jerked  upward  and  then  falls  again.  But  it  does 
not  retm-n  quite  to  its  original  position ;  it  remains 
somewhat  raised,  thus  showing  that  the  muscle  is  now 
continuously  contracted ;  and  this  contraction  lasts  as 
long  as  the  current  passes  iminterruptedly  through  the 
muscle. 

If  the  current  is  interrupted,  a  pulsation  which 
jerks  the  lever  upward  is  sometimes  but  not  always 
observable;  the  muscle  then,  however,  resumes  its 
original  length,  which  it  retains  until  it  is  irritated 
anew. 

2.  These  experiments  show  that  muscle  exhibits 
two  forms  of  contraction :  the  one,  which  we  called  pul- 
sation, is  of  short  duration  ;  the  other,  which  is  produced 
by  a  constant  electric  current,  endm'es  longer.  This 
more  enduring  form  of  contraction  may,  moreover,  be 
yet  more  conveniently  produced  by  allowing  an  irritant 
such  as  in  itself  would  only  produce  a  single  pulsation 


PULSATIOX  AND  TETANUS.  33 

to  operate  repeatedly  in  quick  succession.  An  inductive 
current  is  most  suitable  for  this  purpose,  for  it  can 
be  produced  at  will  by  the  closing  and  opening-  of  an- 
other current.  Once  more  turning  to  the  coils  A  and 
B  (fig.  10,  p.  31),  let  A  be  connected  with  a  chain, 
B  with  the  muscle.  Within  the  circuit  of  the  chain 
which  includes  A,  we  can  insert  an  apparatus  capable 
of  repeatedly  and  rapidly  shutting  or  opening  the 
current.  For  this  purpose  a  so-called  electric  wheel 
is  used.  The  wheel  Z  is  made  of  some  conducting 
substance,  such  as  copper, 
and  its  circumference  is  cut 
into  teeth  like  that  of  the 
ratchet-wheel  of  a  watch. 
The  copper  wire  rests  on 
this  circumference.  The 
axis  of  the  wheel  and  the 

7  ,     1        ..1  I'lt;-  11.     Electric  Wheel. 

Wire  0  are  connected  with 

the  conducting  wires  by  means  of  the  screws  d  and  /. 
When  the  click  rests  on  one  tooth  of  the  circumference 
of  the  wheel,  the  current  is  enabled  to  pass  through 
the  wheel,  and  thus  also  thi-ough  coil  A  ;  it  is,  how- 
ever, interrupted  during  the  interval  which  intervenes 
while  the  click  springs  from  one  tooth  to  the  other. 
Therefore,  by  turning  the  wheel  on  its  axis  the  current 
in  coil  A  is  alternately  closed  and  opened.  Conse- 
quently, inductive  currents  constantly  occur  in  the 
adjacent  coil  B,  and  these  pass  in  rapid  succession 
through  the  muscle.  Each  of  these  currents  irritates 
the  muscle ;  and  since  they  occur  in  such  quick  suc- 
cession, the  muscle  has  no  time  to  relax  in  the  inter^■a]s, 
but  continues  permanently  contracted.  Enduring  con- 
3 


34 


PHYSIOLOGY    OF    MUSCLES    AND   NERVES. 


traction  of  this  sort  is  called  tetanus  of  the  muscle  to 
distinguish  it  from  a  series  of  distinct  pulsations. 

Another  method  of  frequently  and  repeatedly  clo- 
sing and  opening  the  current  is  by  means  of  a  self- 
acting  apparatus  which  is  put  in  motion  by  the  current 
itself.     This,  which  is  called  Wagner's  hammer,  is  re- 
presented in  fig.  12.     The  current  of  the  chain  is  con- 
ducted through  the  column 
represented  on  the  right  to 
the  German  silver  spring  o  o. 
A  small  platinmn  plate  c  is 
soldered  on  to  the  latter,  and 
is  pressed  against  the  point 
above  it  by  the  elastic  force 
of  the  spring.    The  current 
passes  from  this  to  the  coils 
of  a  small  electro-magnet, 
and,  after  passing  through 
this,    back    to    the    chain 
through  the  clamp  connected  with  it  on  the  left.     An 
armature   of   soft  iron,  «,  fastened   on  to  the    spring 
o  o,  is  suspended  over  the  poles  of  the  electro-magnet. 
This  iron  being  attracted  by  the  electro-magnet,  the 
small  plate  c  is  forced  away  from  i  he  point  and  the  cur- 
rent is  thus  interrupted.     In  so  doing,  however,  the 
electro-magnet  parts  with  its  magnetism,  and  conse- 
quently relinquishes  its  hold  upon  the  armature ;  the 
plate    is    thus    again    pressed   by    the    action    of   the 
spring  against  the  point.    The  current  being  thus  again 
closed,  the  electro-magnet  recovers  its  force,  again  at- 
tracts the  armature,  and  again  interrupts  the  current ; 
and  these  processes  are  continued  as  long  as  the  chain 
remains  inserted  between  the  column  on  the  right  and 


Fig.  12.    Wagner's  Hammer. 


PULSATION   AND    TETANUS. 


35 


the  clamp  on  the  left.  In  order  to  use  this  hammer  for 
the  production  of  inductive  currents,  the  one  coil,  A,  of 
the  apparatus  (shown  in  fig.  10,  p.  31),  must  be  inserted 
between  the  two  clamps  shown  on  the  right. ^ 

Wagner's  hammer  in  a  more  simple  form  may  be 
permanently  connected  with  coil  A.  In  this  case  it  is 
best  to  place  the  second  coil  5  on  a  sliding-piece  which 
is  so  arranged  that  it  can  be  moved  along  a  groove  to  a 


Fig.  1[ 


The    sliding    INDVCTIVE    AlTAliAlLs. 

(As  used  bj-  du  Bois-RejTnond.) 


greater  or  less  distance  from  coil  A.  This  enables  the 
operator  to  regulate  the  strength  of  the  inductive  current 
generated  in  it.  Fig.  1 3  represents  an  apparatus  of  this 
sort.  The  secondary  coil,  in  which  the  inductive  currents 
originate,  is  in  this  case  indicated  by  i ;  the  primary  coil, 
through  which  the  constant  currents  pass,  by  c ;  6  is  the 
electro-magnet ;  h  the  armature  of  the  hammer ;  /  is 
a  small  screw,  at  the  point  of  contact  of  which  with  the 

'  In  order  to  set  Wagner's  hammer  itself  in  motion,  these  clamps 
must  be  connected  bj'  a  wire  through  which  alone  tlie  connection 
from  the  point  to  the  coils  of  the  electro- magnet  is  made. 


36 


PHYSIOLOGY    OF    MUSCLES    AND    XERVES. 


small  plate  soldered  on  to  the  surface  of  the  German  ■ 
silver  spring  the  current  is  closed  and  interrupted.  An 
apparatus  of  this  kind  is  called  a  sliding  inductorium. 
It  is  only  necessary  to  attach  the  ends  of  the  coil  i  to 
the  muscle,  and  to  insert  the  chain  between  the  columns 
a  and  g.  The  action  of  the  hammer  then  at  once 
commences  ;  the  inductive  cur- 
rents generated  in  c  pass  through 
the  muscle,  which  contracts  te- 
tauically. 

Instead  of  connecting  coil  c 
immediately  with  the  muscle,  it 
is  better  to  carry  the  wires  from 
1  he  coil  to  the  two  clamps  b  and 
c  in  the  apparatus  shown  in  fig. 
14,  which  is  called  a  tetanising 
hey.  Two  other  wires  pass  from 
these  same  clamps  h  and  c  to  the 
muscle.  When  the  inductive  ap- 
paratus is  in  action  the  muscle  is 
put  into  a  tetanic  condition.  But 
as  soon  as  the  lever  d  is  pressed 
down,  so  as  to  connect  h  and  c 
together,  the  current  of  coil  i  is 
Fig.  14.  Tetanising  key  of  enabled  to  pass  through  this  le- 

DU   BoiS  ReYMOSD.  rpi         1  7  u     •  J         r 

ver.  Ihe  lever  a  being  made  or 
a  short  and  thick  piece  of  brass,  which  offers  hardly  any 
resistance  to  the  current,  while  the  muscle  on  the  con- 
trary offers  great  resistance,  very  little  of  the  current 
passes  through  the  muscle,  but  nearly  all  through  the 
lever  d.  The  muscle,  therefore,  remains  at  rest.  As 
soon,  however,  as  the  lever  d  is  again  raised,  the  inr 
ductive  currents  must  again  pass  through  the  muscle. 


ACCOMPLISHMENT    OF    LABOUR.  37 

A  slight  pressure  on  the  handle  of  the  lever  d  is,  there- 
fore, suflQcient  to  produce  or  to  put  an  end  to  the  te- 
tanic condition  at  the  will  of  the  operator,  thus  allowing 
more  accurate  study  of  the  muscle  processes. 

We  have  now  noticed  muscle  in  two  conditions  :  in 
the  ordinary  condition  in  which  it  usually  occurs  either 
within  the  body  or  when  taken  from  the  body,  and  in 
the  contracted  condition  which  results  from  the  appli- 
cation of  certain  irritants.  The  former  condition  may 
be  spoken  of  as  the  rest  of  the  muscle,  the  latter  as  the 
action  of  the  muscle.  Muscular  action  occm*s  in  two 
forms,  one  of  which  is  a  sudden  temporary  shortening 
or  pulsation,  while  the  other  is  an  enduring  contraction 
or  tetanus.  The  latter,  on  account  of  its  longer  dura- 
tion, is  more  easily  studied.  In  many  cases  it  is  a 
matter  of  indifference  whether  pulsating  or  tetanised 
muscle  is  examined.  In  the  following  investigations 
we  shall  therefore  employ  sometimes  one,  sometimes 
the  other,  method  of  irritation. 

3.  On  attaching  weights  to  a  muscle,  the  latter  is 
capable  of  raising  these  weights  so  soon  as  it  is  set  in 
motion.  It  raises  the  weight  to  a  certain  height,  and 
thus  accomplishes  labour  which,  in  accordance  with 
mechanical  principles,  can  be  expressed  in  figures  by 
multiplying  together  the  weight  raised  and  the  height 
to  which  it  is  raised.  This  height  to  which  the  weight 
can  be  raised,  which  may  be  called  the  height  of  ele- 
vation of  the  muscle,  can  be  measured  by  means  of  the 
myograph  already  described.  On  attaching  a  weight 
to  the  lever  of  the  myograph,  the  muscle  is  imme- 
diately extended.  The  pencil  must  now  be  brought  in 
contact  with  the  glass  plate  of  the  myograph,  and 
the  muscle  must  be  made  to  contract  by  opening  the 


38  PHYSIOLOGY    OF.  MUSCLES   AND   NERVES. 

key  so  as  to  allow  the  inductive  currents  to  have  access 
to  the  muscle.  The  latter  at  once  shortens,  and  its 
height  of  elevation  is  indicated  by  a  vertical  stroke  on 
the  smoked  glass  plate.  On  instituting  a  series  of 
experiments  with  the  same  muscle  but  with  various 
weights,  it  will  be  found  that  the  muscle  is  not  able 
to  raise  all  weights  to  the  same  height.  When  the 
weight  is  small  the  height  to  which  it  is  raised  is  great. 
As  a  rule,  as  the  weight  increases,  the  height  to  which 
it  is  raised  becomes  less,  and  finally,  when  a  certain 
weight  is  reached,  it  becomes  unnoticeable.     Fig.  15 


"  "  ■»  i  „ 

250 
Fig.  15.    Height  of  elevation  coxseqdent  on  the  application  of 
varying  weights. 

shows  the  result  of  a  series  of  experiments  of  this  sort. 
The  figures  under  each  of  the  vertical  strokes  represent 
in  grammes  the  amount  of  the  weight  raised ;  the  height 
of  the  strokes  is  double  the  real  height  of  elevation, 
the  apparatus  employed  in  the  experiment  representing 
them  twice  their  natural  size.  Between  each  two  of 
the  experiments  the  glass  plate  was  pushed  on  a  little 
further  in  order  that  the  separate  experiments  might 
be  indicated  side  by  side.  In  finding  the  first  of 
these  heights  of  elevation,  under  which  stands  an  0,  no 
weight  was  applied,  and  even  the  weight  of  the  indi- 
cating lever  was  neutralised  by  an  equivalent  weight. 
It  appears,  therefore,  that  the  height  of  elevation  is 


INTERNAL    WORK    DURING   TETANUS.    .  39 

greatest  in  this  case.  Each  of  the  succeeding  heights 
begins  from  a  somewhat  lower  point  in  consequence  of 
the  extension  of  the  muscle  by  the  applied  weights. 
But  each  also  rises  to  a  less  height  than  that  which 
preceded  it ;  and,  finally,  a  weight  of  250  grammes 
being  applied,  the  height  of  elevation  is  naught. 

From  this  series  of  experiments  it  is  evident  that, 
as  the  weight  increases,  the  height  to  which  it  is  raised 
continually  decreases.  The  following  conclusion  must, 
therefore,  be  drawn  as  to  the  work  accomplished  by  the 
.muscle.  When  no  weight  is  apphed,  the  height  of 
elevation  is  great ;  but  as  no  Aveight  is  raised  in  this 
case,  the  amount  of  work  accomplished,  therefore,  also 
equals  0.  When  250  grammes,  the  greatest  weight,  is 
applied,  the  height  of  elevation  equals  0,  so  that  in 
this  case  also  no  work  is  accomplished.  It  was  only  on 
the  application  of  the  intermediate  weights  that  the 
muscle  accomplished  work ;  and  this,  moreover,  at  first 
increased  until  a  weight  of  150  grammes  was  reached, 
and  then  gradually  decreased.  On  calculating  the 
amount  of  work  accomplished  during  each  of  the  pul- 
sations in  question,  the  following  results  are  found : — 

Weight  applied.  .  0 
Height  of  elevation  .  li 
Work  accompli^jhed  .     0 

The  same  results  may  be  obtained  with  any  other 
muscle.  So  that  it  may  be  stated  as  a  very  general 
proposition,  that  for  each  muscle  there  is  a  definite 
weight,  on  the  application  of  which  the  greatest  amount 
of  work  is  accomplished  by  that  muscle  ;  when  greater 
or  less  weight  is  applied,  the  amount  of  work  accom- 
plished is  less.  But  the  height  of  elevation  correspond- 
ing with  the  application  of  one  and  the  same  weight  is 


50 

100 

150 

200 

250  gr. 

9 

7 

5 

2 

0  mm. 

450 

700 

750 

400 

0  mm. 

40,  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

not  always  the  same  in  the  case  of  dififerent  muscles.  On 
comparing  thick  with  thin  muscles,  it  appears,  in  the  first 
place,  that  the  extension  in  the  case  of  thick  muscles  be- 
comes less  in  proportion  as  the  weight  applied  increases ; 
and  that  the  decrease  in  the  height  of  elevation  corre- 
sponding to  the  increase  in  the  weight  applied  proceeds 
less  rapidly ;  so  that  much  greater  weights  can  be  raised 
by  thick  than  by  thin  muscles.  On  the  other  hand,  it 
appears  that  in  the  case  of  muscles  of  equal  thickness 
the  height  of  elevation  is  greater  in  proportion  as 
the  muscle-fibres  are  longer.  Under  an  equal  weight 
the  height  of  elevation  increases  proportionately  with 
the  length  of  the  muscle-fibres.  They  decrease  with 
increased  weight;  and  they  do  this  more  rapidly  in  the 
case  of  thin  than  of  thick  muscles. 

4.  In  calculating  the  amount  of  work  accomplished 
by  a  muscle,  only  the  raising  of  the  weight  is  taken  into 
consideration.  When,  however,  the  ordinary  method 
of  irritating  the  muscle  is  applied,  the  weight  which 
is  raised  sinks  back  after  each  pulsation  to  its  former 
height.  The  muscular  work  accomplished  at  each  pul- 
sation is,  therefore,  cancelled.  It  is  probably  converted 
into  warmth.  It  is,  however,  possible  to  retain  the 
weight  at  the  height  to  which  it  was  raised  by  the  muscle. 
A.  Fick  accomplished  this  very  ingeniously  by  causing 
the  muscle  to  act  on  a  light  lever,  which  moves  a  wheel 
each  time  it  rises,  but  leaves  the  same  wheel  undis- 
turbed when  it  again  sinks.  A  thread,  on  which  the 
weight  hangs,  passes  over  the  axis  of  the  wheel.  The 
effect  of  this  arrangement  is  that  the  muscle  at  each 
pulsation  turns  the  wheel  slightly,  and  thus  slowly 
raises  the  weight.  If  the  muscle  is  made  to  pulsate 
frequently,  the  weight  is  raised  somewhat  higher  each 


GENERATION    OF   WARMTH.  41 

time,  and  the  final  result  is  the  sum  of  the  work 
accomplished  by  the  separate  pulsations.  Fick  calls 
this  apparatus  a  labour-accumulator  (^Arheitaann'mler). 
It  rejjresents  the  method  by  which  the  whole  work  of 
all  muscular  efforts  is  summarised.  When  labourers 
lift  a  weight  by  means  of  a  winch  or  windlass,  a  cog- 
wheel and  drag-hook  is  applied  to  the  axis  in  such 
a  way  that  the  wheel  is  free  to  revolve  in  one  direc- 
tion but  not  in  the  other.  This  gives  cumulative 
effect  to  the  separate  muscular  efforts  which  raise  the 
weight;  and  the  labourer  is  even  able  to  make  longer 
or  shorter  pauses  without  the  result  of  the  work  already 
accomplished  being  cancelled  by  the  falling  back  of  the 
weight. 

In  tetanus  the  case  is  not  the  same  as  in  separate 
pulsations.  In  the  former  the  muscle  at  first  accom- 
plishes work  by  raising  the  weight,  and  then  prevents 
it  from  falling  by  its  own  exertion.  In  addition  to 
the  height  of  elevation,  it  is,  therefore,  possible  to 
•distinguish  also  the  carried  height,  that  is  to  say,  the 
height  at  which  the  weight  is  permanently  supported. 
In  doing  this  the  muscle  does  not  really  accomplish 
any  work  in  the  mechanical  sense ;  for  work  consists 
only  in  the  raising  of  weight.  In  lifting  a  stone  to  the 
height  of  the  table  I  accomplish  definite  work;  the 
stone  being  placed  on  the  table  presses  by  its  own 
weight  on  the  latter  ;  but  the  table  though  it  prevents 
the  stone  from  falling,  cannot  be  said  in  so  doing  to  ac- 
complish work.  So  it  is  in  the  case  of  piuscle.  On  raising 
a  weight  by  means  of  the  muscles  of  my  arm  to  the 
height  of  my  shoulder,  and  then  holding  out  my  arm 
horizontally,  the  muscles  of  the  arm  prevent  the  weight 
from  ftilling  ;  they  act  just  as  the  table,  and,  therefore, 


42  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

they  accomplish,  no  work  in  a  mechanical  sense.  Yet 
everyone  knows  the  difficulty  of  holding  a  weight  long 
in  this  position ;  the  sense  of  weariness  which  very 
soon  makes  itself  felt  shows  that  work  in  a  physiological 
sense  is  really  done.  The  kind  of  work  thus  accom- 
plished may  be  spoken  of  as  the  internal  work  of  the 
muscle,  as  distinguished  from  the  external  work  accom- 
plished in  the  raising  of  weights. 

5.  We  must  now  inquire  on  what  the  labour  accom- 
plished by  the  muscle  as  a  whole  depends.  We  are 
justified  in  assuming  that  here  also,  as  in  other  cases, 
the  work  done  does  not  originate  in  itself,  but  comes 
into  existence  in  consequence  of  the  exercise  of  some 
force.  On  examining  a  muscle  during  its  active  con- 
dition, we  find  that  chemical  processes  occur  wit! in  it 
which,  though  the  details  are  not  indeed  fully  known, 
must,  since  they  are  connected  with  the  production 
of  warmth  and  the  evolution  of  carbonic  acid,  depend 
on  the  oxidation  of  a  portion  of  the  muscle-substance. 
Thus,  the  muscle  acts  like  a  steam-engine,  in  which  work 
is  accomplished  in  the  same  way  by  the  evolution  of 
warmth  and  the  production  of  carbonic  acid.  So  far  all 
is  clear;  a  portion  of  the  substances  of  which  the 
muscle  is  composed  is  oxidised  during  its  active  state, 
and  the  energy  released  by  this  chemical  process  is 
the  source  of  the  work  accomplished  by  the  muscle. 
The  production  of  warmth  in  a  muscle  can  be  shown 
even  during  a  single  pulsation;  but  this  production 
of  warmth  is  far  more  noticeable  during  tetanus ; 
and  as  warmth  is  but  another  form  of  motion,  we  may 
infer  from  this  that  the  whole  force  resulting  from 
the  chemical  process  is  converted  into  warmth  during 
tetanus ;  while  during  the  raising  of  a  weight  at  the 


THE    MUSCLE-NOTE.  43 

commencement  of  the  tetanic  condition,  or  during  each 
distinct  pulsation,  a  portion  of  this  force  occurs  in  the 
form  of  mechanical  work. 

There  is  yet  another  fact  which  shows  that  internal 
motion  must  proceed  within  the  muscle  when  con- 
tracted in  tetanus,  notwithstanding  the  quiescent  con- 
dition in  which  externally  it  apparently  is.  A  muscle 
when  in  this  condition  produces  a  sound  or  note.  On 
placing  an  ear-trumpet  on  any  muscle,  for  instance,  on 
that  of  the  upper  arm,  and  then  causing  the  muscle  to 
contract,  a  deep  buzzing  noise  is  audible.  This  may 
also  be  loudly  and  distinctly  heard  on  stopping  the 
outer  ear-passages  with  waxen  plugs,  and  then  contract- 
ing the  muscles  of  the  face ;  or  by  inserting  the  little 
finger  firmly  in  the  outer  ear-passage  and  then  contract- 
ing the  muscles  of  the  arm.  In  the  latter  case  the 
bones  of  the  arm  conduct  the  muscle-note  to  the  ear. 
This  muscular  note  clearly  shows  that  vibrations  must 
occur  within  the  muscle,  however  apparently  unchanged 
the  form  of  the  latter  may  be.  We  found  that  teta- 
nus thus  apparently  constant  is  induced  by  distinct 
irritants  aj)plied  in  quick  succession.  Helmholtz  has 
shown  that  each  of  these  irritations  really  corresponds 
with  a  vibration;  for,  if  the  number  of  the  distinct 
irritations  is  altered,  the  muscle-note  is  also  changed, 
the  height  of  the  muscle-note  always  corresponding 
exactly  with  the  number  of  irritants  applied.  Though, 
therefore,  no  alteration  in  form  can  be  perceived  in  the 
tetanised  muscle,  this  can  only  be  due  to  the  fact  that 
movements  which  occur  among  the  particles  within  the 
muscle  effect  the  note,  though  the  external  form  re- 
mains unchanged.  A  somewhat  similar  phenomenon 
is  observable  in  rods  when  caused  to  vibrate  longitu- 


44  PHYSIOLOGY    OF    MUSCLES   AND   NERVES. 

dinally ;  for  these  also  emit  a  sound  although  no  change 
of  form  is  externally  perceptible. 

This  raises  a  question  as  to  how  many  of  these  irri- 
tations are  really  requisite  in  order  to  bring  a  muscle 
into  an  enduring  condition  of  contraction.  By  means  of 
Wagner's  hammer  (fig.  12),  just  described,  or  by  means 
of  an  electric  wheel  (fig.  11),  the  number  of  the  irrita- 
tions may  be  regulated.  It  will  be  found  that  from  1 6  to 
18  distinct  irritations  in  each  second  are  quite  sufficient  to 
cause  a  constant  contraction  of  the  muscle.  In  a  living 
body  also,  where  the  muscles  are  voluntarily  contracted, 
the  condition  of  tetanus  appears  to  be  produced  by  the 
same  number  of  irritations.  It  has  been  found  that  the 
height  of  the  muscle-note  heard  duiing  voluntary  con- 
traction of  the  muscles  is  about  equal  to  c*  or  cZ',  which 
represents  from  32  to  36  vibrations  in  the  second.  But 
Helmholtz  was  able  to  show,  with  great  probability, 
that  this  is  not  the  true  number  of  muscle-vibrations, 
but  that  the  vibrations  within  the  muscle  are  really 
only  half  as  many.  As,  however,  notes  of  this  pitch 
are  indistinguishable  to  our  ears,  we  hear  the  next 
higher  tone  instead,  which  represents  twice  the  num- 
ber of  vibrations.^ 

6.  As  yet  we  have  noticed  only  the  shortening  of 
muscles.  This  alone  determines  the  amount  of  labour 
accomplished,  which  consists  in  raising  weights.  But 
on  looking  at  a  contracted  muscle,  it  is  evident  that 
it  has  become,  not   only  shorter,  but  thicker.      This 

'  According  to  Preyer,  some  men  are  capable  of  distiuguisbing 
notes  of  as  many  as  fifteen  to  twenty-five  vibrations  per  second ; 
and,  according  to  the  same  authority,  the  muscle-note  sounds  very 
like  that  produced  by  from  eighteen  to  twenty  vibrations  per 
second,  which  corresponds  very  well  with  the  views  of  Helmholtz 


ALTERATION    IN    FORM    DURING    CONTRACTION.         45 

raises  the  question  whether  the  muscle  in  contracting 
has  undergone  no  change  in  the  amount  of  space  oc- 
cupied by  it,  or  if  its  mass  has  become  more  dense. 
It  is  not  easy  to  detei'mine  this  accurately,  for  the 
alteration  in  the  volume  of  the  muscle  can  only  be 
very  slight.  Experiments  which  have  been  made  by 
P.  Erman,  E.  Weber,  and  others,  agree  in  showing 
that  a  very  slight  diminution  in  the  muscle  does  cer- 
tainly take  place. 

Eemembering,  however,  that  muscle  consists  of  a 
moist  substance,  and  that  about  three-fourths  of  its 
whole  weight  is  water,  even  this  slight  decrease  in 
volume  must  be  the  result  of  very  considerable  pressure 
— for  fluids  are  extremely  difl&cult  of  compression — un- 
less possibly  a  portion  of  the  water  is  expressed  through 
the  pores  of  the  sarcolemma  pouch. 

More  important  than  this  structural  change  of  the 
whole  muscle  is  the  change  of  form  which  each  separate 
muscle-fibre  undergoes.  This  may  be  observed  under 
the  microscope  in  thin  and  flat  muscles,  when  it  will 
be  found  that  each  muscle-fibre  also  becomes  both 
shorter  and  thicker.  On  placing  a  muscle  on  a  glass 
plate  under  the  microscope,  in  order  to  observe  this, 
the  muscle,  when  the  irritant  ceases  to  act,  is  seen  to 
remain  apparently  in  its  shortened  form.  But  the 
separate  muscle-fibres  resume  their  former  length  as 
soon  as  the  irritant  ceases,  and  they  therefore  lie  in  a 
zigzag  position  until  they  are  straightened  by  some 
external  force.  I  merely  mention  this  here,  because 
the  phenomenon  is  of  historic  interest.  Prevost  and 
Dumas,  who  were  the  first  to  examine  this  condition, 
believed  that  the  contraction  of  the  whole  muscle  was 
due  to  this  zigzag  bending  of  the  muscle-fibres.     With 


46  PHYSIOLOGY    OF    MUSCLES   AND   NEfiVES. 

the  incomplete  apparatus  which  they  were  then  alone 
able  to  command,  they  were  unable  to  induce  an  en- 
dm-ing  irritation  of  the  muscle ;  and  they,  therefore, 
confused  the  state  of  relaxation  with  that  of  contrac- 
tion. 


CHAPTER    IV. 

1.  Alteration  in  elasticity  during  contraction  ;  2.  Duration  of  con- 
traction ;  tlie  myograph ;  3,  Determination  of  electric  time  ; 
4.  Application  of  this  to  muscular  pulsation  ;  5.  Burden  and 
overburden— muscular  force ;  6.  Determination  of  muscular 
force  in  man ;  7.  Alteration  in  muscular  force  during  contrac- 
tion. 

1.  We  now  approach  one  of  the  most  remarkable  of 
the  facts  connected  with  the  general  physiology  of  the 
muscles :  this  is  the  alteration  in  the  elasticity  of  a 
muscle  during  its  contraction.  Even  E.  Weber,  who 
first  penetrated  deeply  in  his  researches  into  the  sub- 
ject of  muscular  contraction,  showed  that  muscle  is 
further  extended  by  the  same  weight  when  it  is  in  a 
state  of  activity  than  when  it  is  quiescent.  This  is  the 
more  striking  because  the  muscle  becomes  shorter  and 
thicker  during  its  activity,  so  that  it  should  conse- 
quently be  less  extended  ;  for,  as  we  found,  the  exten- 
sion by  a  definite  weight  is  greater  in  proportion  as  the 
body  extended  is  longer,  and  is  less  in  proportion  as  the 
body  extended  is  thicker.  If,  therefore,  an  active  muscle 
is  further  extended  than  one  that  is  inactive  by  the  same 
weight,  this  can  only  be  due  to  a  change  in  its  elasti- 
city. It  is  hard  to  say  how  this  occurs.  The  pheno- 
mena of  contraction  may,  however,  be  explained  by 
saying  that  muscle  has  two  natural  forms  :  one  proper 


48 


PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 


to  it,  when  it  is  in  a  quiescent  state  ;  the  other,  when 
it  is  active.  When  a  quiescent  muscle  is  brought  into 
an  active  condition  by  irritation,  it  assumes  a  form 
which  is  no  longer  natural  to  it,  it  strives  to  attain  the 
latter,  and  shortens  until  it  reaches  its  new  form,  which 
is  then  natural  to  it.  If  the  muscle  is  extended  by  a 
weight,  and  is  then  irritated,  it  immediately  contracts ; 
but  only  to  that  length  which  represents  the  exten- 
sion by  the  attached  weight,  proper  to  its  new  form. 
Let  us  imagine  that  A  B,  in  fig.  16,  is  the  length  of 


J      A' 


J'" 


r 

r' 

I" 

d" 

C" 

d'" 

^ 

r 

zr^ 

.^____^ 

^^^,„^^^ 

// 

"~-~ — - 

- —  ^~~~~^-- 

Fig.  16.    Alteration  in  Ela.sticitv  during  conteactiox. 

the  muscle  when  quiescent  and  unburdened,  and  that 
J.  6  is  the  length  of  the  muscle  when  active  and  un- 
bm'dened.  Then  the  muscle,  if  it  is  irritated  while 
unweighted,  will  shorten  to  the  extent  represented  by 
AB— Ah  =  bB;  b  B  is,  therefore,  the  height  of 
elevation  of  the  unweighted  muscle.  If  a  weight  p  is 
attached  to  the  nauscle,  the  latter  in  its  inactive  condi- 
tion will  be  extended  to  a  certain  degree  (B^  d') ;  so 
that  its  length  will  now  be  A  B  +  B'd'=  A'  B'.  On 
being  now  irritated,  it  contracts  and  assumes  a  lenofth 


ALTERATION    IX    FORM    DURING    CONTliACTION.         49 

which  must  equal  A  B  +  ch'  =  A'  V,  in  which  A  h  is 
the  natural  length  of  the  active  muscle  when  un- 
weighted, and  c  h'  is  the  extension  which  the  active 
muscle  undergoes  on  the  application  of  the  same  weight 
p.  A'  B'—A'V=h'  B'  is,  therefore,  the  height  of 
e'evation  of  the  muscle  when  the  weight  jp  is  applied. 
Now,  our  former  experiments  have  shown  that  the 
height  of  elevation  decreases  as  the  weight  increases. 
The  height  of  elevation  h  B,  when  the  weight  apphed 
=  0,  is,  therefore,  greater  than  the  height  of  elevation 
h'  B\  with  the  weight  -p.  It  therefore  follows  that  the 
extension  c  h'  must  be  greater  than  the  extension  d'  B' ; 
or,  in  other  words,  the  same  weight,  ]),  extends  the 
muscle  more  when  the  latter  is  active  than  when  it 
is  quiescent.  Calculating  on  this  principle  the  curves 
of  the  extension  of  the  active,  as  well  as  of  the  in- 
active, muscle,  for  the  first  we  iind  the  curve  b  b'  y; 
for  the  second  the  curve  B  B'  x;  and  these  two  con- 
tinue gradually  to  approach  each  other,  until  they  at 
last  cut  each  other  at  the  point  jB'^.  This  point  5'% 
which  corresponds  with  the  weight  p,  shows  that  when 
this  weight  is  applied,  the  length  of  the  active  and 
the  inactive  muscles  is  equal.  If,  therefore,  when  the 
weight  p  is  applied,  the  muscle  is  irritated,  the  height 
of  elevation  is  nothing.  The  muscle  is  incapable  of 
raising  this  weight,  a  fact  which  we  have  already  noticed 
in  previous  experiments.^ 

Yet  another  point  of  great  interest  is  observable  in 
studying  this  alteration  in  the  elasticity.  When  a  cer- 
tain weight,  I;  is  applied,  the  extension  of  the  active 
muscle  =  c'  b" :  that  is,  the  active  muscle,  when  this 
weight  is  applied,  assumes  exactly  the  length  proper  to 
'  See  Notes  and  Additions,  No.  1. 


50  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

the  quiescent  muscle  when  unweighted.  If  an  experi- 
ment is  successfully  arranged  so  that  an  inactive  muscle 
is  not  extended  by  the  weight  k — by  fastening  the  latter 
to  the  muscle,  but  immediately  supporting  it,  so  that 
it  does  not  extend  the  muscle — and  if  the  muscle  is 
then  irritated,  it  is  evident  that  the  muscle  is  incapable 
of  raising  this  weight  from  its  support.  By  finding  the 
weight  which  is  exactly  sufficient  to  effect  this,  it  is 
evident  that  we  shall  find  an  expression  for  the  magni- 
tude of  the  energy  with  which  the  muscle  strives  to 
pass  from  its  natural  into  a  contracted  condition.  This 
energy  is  called  the  force,  of  the  muscle.  A  method  of 
accurately  determining  this  will  presently  be  explained. 

2.  As  far  as  it  is  possible  to  examine  the  matter, 
the  condition  of  muscles  during  their  distinct  pulsations 
is  exactly  as  in  tetanus.  All  that  has  been  said  of  the 
height  of  elevation,  and  of  the  accomplishment  of  la- 
bour dependent  on  this,  and  of  the  alteration  in  the 
elasticity,  is  as  true  of  distinct  pulsations  as  of  the 
tetanic  condition.  But  it  is  very  hard  to  observe  the 
alteration  in  form  during  the  very  short  time  which  is 
occupied  by  one  of  these  pulsations.  Means  of  drawing 
very  accurate  conclusions  even  on  this  point  have,  how- 
ever, been  found,  especially  since  Helmholtz  turned  his 
attention  to  the  matter,  in  1852. 

Various  methods  are  employed  in  experimental  re- 
search to  measure  very  short  periods  of  time  accurately, 
and  to  study  processes  which  occur  even  within  the 
shortest  periods.  Not  only  has  the  speed  of  the  cannon- 
ball  during  the  various  periods  of  its  passage  from  the 
mouth  of  the  cannon  to  its  arrival  at  its  destination 
been  measured,  but  this  has  also  been  done  in  the  case 
of  the  yet  shorter  time  occupied  by  the  explosion  of 


DURATION   OF   rULSATIO]S\  51 

gunpowder.  The  duration  of  the  electric  spark  alone 
yet  remains  unmeasured.  This  may,  therefore,  be  re- 
garded as  really  instantaneous,  or  at  least  as  occupying 
a  time  shorter  than  any  measurable  period.  Some 
observers  have  estimated  its  duration  as  less  than 
24 oTo"  of  a  second. 

The  most  serviceable  means  of  measuring  very 
short  periods  is  by  causing  the  process  to  be  measured 
to  register  itself  on  a  rapidly  moved  surface,  or  by 
using  an  electric  cm'rent  the  action  of  which  depends 
on  a  magnet  as  regards  its  duration.  Each  of  these 
methods  has  been  applied  to  muscle. 

Supposing  a  smooth  surface,  such  as  a  glass  plate, 
moved  with  great  rapidity  in  its  own  plane,  then  a 
pointed  wire  turned  at  right  angles  to  the  plate  will 
mark  a  straight  line  on  the  latter.  If  the  plate  has 
been  smoked  this  line  will  be  visible.  Supposing  the 
wire  is  attached  to  an  instrument  vibrating,  like  a 
tuning  fork,  upward  and  downward,  then  the  line 
drawn  by  the  pencil  when  the  plate  is  moved  will  be 
not  straight  but  waved.  As  the  number  of  the  vibra- 
tions may  be  told  from  the  note  which  the  vibrating 
instrument  emits,  it  is  known  that  the  distance  be- 
tween each  two  waves  of  the  waved  line  obtained 
represents  a  certain  period  of  time.  Assuming  that  the 
instrument  makes  250  vibrations  in  each  second,  it 
is  evident  that  the  plate  must  have  moved  the  dis- 
tance between  each  two  waves  in  -^-^  of  a  second. 
Now,  if  it  is  possible  to  cause  a  muscle-pulsation  to 
register  itself  on  the  same  plate,  then  from  the  distance 
of  the  separate  parts  of  the  line  thus  registered,  when 
compared  with  the  waves  drawn  by  the  vibrating 
instrument,  the  duration  of  time  may  be  accurately 


52 


PHYSIOLOGY    OF   MUSCLES   A]MD   NERVES. 


determined.     The  myograph  of  Helmholtz  depends  on 
this  principle.     Originally  it  consisted  of  a  glass  cylin- 


FiG.  17.    Myograph  of  Helmholtz. 

(One  quai-ter  natural  size.) 

der  which  rotated  rapidly  on  its  own  axis.     The  appa- 
ratus has,  however,  since  undergone  many  alterations. 


THE    MYOGKAPH.  53 

Fig.  17  represents  it  in  the  form  given  to  it  by  du  Bois- 
Reymond.  The  clockwork-  enclosed  in  the  case  c  sets 
the  cylinder  A  in  rotation.  A  heavy  disc  B  is  fastened 
on  to  the  axis  of  the  cylinder,  on  the  lower  surface  of 
which  are  certain  brass  wings  arranged  vertically  and 
immersed  in  oil.  This  oil  is  contained  in  the  cylin- 
drical vessel  B'.  By  raising  or  lowering  this  vessel  the 
amount  of  resistance  offered  to  the  rotatory  motion 
may  be  gi'aduated.  This,  together  with  the  great 
weight  of  the  heavy  plate  B,  causes  the  rate  of  rotation 
of  the  cylinder  A  to  increase  but  very  slowly.  As 
soon  as  a  proper  speed  has  been  attained,  the  muscle 
is  irritated ;  and  this,  on  contracting,  raises  the  lever  c 
so  that  the  point  e  fastened  to  the  latter  traces  a  curve 
on  the  cylinder. 

To  carry  out  the  experiment,  the  muscle  is  fastened 
in  a  vice  within  the  glass  case,  so  as  to  prevent  its 
drying  up,  and  is  then  connected  with  the  lever  c ;  the 
cylinder  A  is  covered  with  a  coating  of  soot,  and  is  then 
firmly  fastened  on  its  axis ;  the  pointed  indicator  is 
brought  into  contact  with  the  cylinder  by  means  of 
the  tliread  /.  When  this  cylinder  is  slowly  turned 
round  by  the  hand,  a  horizontal  line  is  inscribed  on  it 
by  the  indicator,  and  this  represents  the  natural  length 
of  the  quiescent  muscle.  On  the  circumference  of 
the  disc  B  is  a  projection  called  the  'nose.'  When 
the  disc  together  with  the  cylinder  connected  with  it 
are  in  a  certain  position,  this  nose  touches  the  bent 
bayonet-shaped  angled  lever  I.  When  the  latter  is 
turned  aside  it  raises  the  lever  h  by  means  of  the  arm 
t,  thus  breaking  the  contact  of  a  current  between  the 
lever  and  the  small  column  standing  in  front  of  it.  The 
current  of  an  electric  chain  is  conducted  throusfh  this 


54  PHYSIOLOGY    OF    MUSCLES    AND    NEEVES. 

point  of  contact,  and  also  through  the  primary  coil  of 
an  inductive  apparatus.  The  secondary  coil  is  con- 
nected with  the  muscle.  When,  therefore,  the  lever  I 
is  turned  aside,  the  muscle  is  irritated.  Accordingly  it 
pulsates  and  raises  the  pencil  of  the  index  so  that  the 
latter  marks  a  vertical  line,  representing  the  height  of 
elevation  of  the  muscle,  on  the  cylinder  A.  By  press- 
ing the  finger  on  g^  the  bayonet-shaped  point  I  may  be 
slightly  raised,  the  index  point  e  being  at  the  same  time 
slightly  removed  from  the  cylinder.  The  clockwork 
is  then  set  in  motion.  The  cylinder  turns,  at  first 
slowly,  but  gradually  more  quickly ;  but  the  muscle 
remains  inactive,  and  the  point  can  make  no  mark. 
As  soon  as  the  cylinder  has  attained  the  desired  speed 
the  finger  is  removed ;  I  sinks,  and  is  soon  after  caught 
and  turned  aside  by  the  nose,  and  the  muscle,  thus  irri- 
tated, pulsates,  and  this  pulsation  is  recorded  on  the 
cylinder  during  its  rotation. 

The  irritation  of  the  muscle  being  efi"ected  by  the 
"  apparatus  itself,  it  occurs  when  the  rotating  cylinder 
is  in  a  definite  position  ;  that  is  to  say,  the  cylinder 
is  in  that  position  in  which  the  nose  has  just  touched 
the  end  of  the  lever  I.  It  is  evident  that  this  posi- 
tion is  the  same  as  that  at  which  the  muscle  was  at 
first  allowed  to  pulsate  when  the  cylinder  stood  still. 
The  vertical  line  then  drawn,  therefore,  indicates 
exactly  the  position  of  the  cylinder  at  the  moment  at 
which  irritation  takes  place.  Where  this  vertical  line 
deviates  from  the  horizontal  line  first  drawn  is  the 
point  at  which  the  pencil  was  when  irritation  was  in- 
duced in  the  muscle.  The  distances  from  which  the 
periods  are  to  be  calculated  must  be  measured  from 
this  point. 


TKE   ]VIYOGEAFH.  55 

In  order  to  make  the  calculation,  the  rate  of  rota- 
tion of  the  cylinder  must  be  accurately  known,  as 
uniformity  in  the  time  of  registration  of  vibrations  is 
not  effected  by  the  apparatus.  As  we  have  already 
seen,  the  rate  of  rotation  of  the  cylinder  is  not  uniform, 
but  increasing ;  owing,  however,  to  the  weight  of  the 
disc  B  and  of  the  immersion  in  oil,  the  increase  is  very 
gradual,  and  when  a  certain  speed  has  been  attained 
the  resistance  offered  by  the  oil  is  so  great  that  no 
further  increase  occurs  and  the  speed  remains  constant. 
By  means  of  the  hand  on  the  face  d  this  speed  can  be 
determined ;  and  it  is  easy  to  cause  the  cylinder  to 
make  exactly  one  revolution  per  second  by  adjusting 
the  oil  vessel  of  the  apparatus. 

The  desired  speed  having  been  attained,  it  is  only 
necessary  to  know  the  circumference  of  the  cylinder  in 
order  to  calculate  the  time  value  of  that  which  is 
marked  on  the  cylinder.  In  order  to  facilitate  the 
measurement  of  the  separate  portions  of  the  cm-ve, 
the  cylinder,  after  being  carefully  removed  from  its 
axis,  must  be  fastened  into  a  suitable  forked  handle 
(such  as  is  represented  in  the  left-hand  lower  corner  of 
fig.  17,  where  it  is  marked  U),  and  the  cylinder  must 
then  be  rolled  on  a  sheet  of  moistened  gelatine  paper. 
The  whole  layer  of  soot  adheres  to  the  sticky  gelatine  ; 
and  the  whole  must  then  be  fastened  with  the  blackened 
side  downward  on  to  a  white  ground.  The  described 
curves  will  then  appear  in  white  on  a  black  ground, 
and  will  admit  of  easy  measurement. 

Fig.  18  is  accurately  copied  from  a  curve  described 
in  this  way  by  the  calf-muscle  of  a  frog.  The  point  at 
which  the  irritation  occurred  is  marked  z.  It  will  at 
once  strike  the  observer  that  the  rising  of  the  indicator 


56  PHYSIOLOGY    OF    MUSCLES   AND   NERVES. 

did  not  begin  at  the  point  z^  but  at  some  little  distance 
beyond  this,  at  a.  From  this  it  is  to  be  inferred  that 
the  contraction  of  the  muscle  did  not  begin  at  the 
moment  of  irritation,  for  it  is  evident  that  the  cylinder 
of  the  myograph  had  time  to  turn  from  z  to  a  before 
the  indicator  was  raised  by  the  contraction  of  the 
muscle.  A  certain  time,  therefore,  elapses  before  the 
change  produced  in  the  muscle  by  irritation  results  in 
contraction.  The  duration  of  this  time — which  can  be 
accurately  calculated  from  the  length  of  the  space  exist- 
ing between  z  and  a — is  about  one-hundredth  of  a 


X  u  c 

Fig.  18.    The  cuuvks  of  a  jiuscle-pui.satiox. 

second.  This  stage  is  called  that  of  latent  irritation^ 
for  during  it  the  irritation  has  not  yet  become  actively 
efficient  in  the  muscle.  From  the  point  a  the  muscle 
evidently  contracts,  as  is  shown  by  the  rising  'of  the 
pencil  from  point  a  to  point  h,  which  is  the  highest 
part  of  the  curve  described  ;  from  that  point  onward 
the  muscle  again  lengthens  till  it  resumes  its  original 
length  at  the  point  c.  The  time  which  elapses  between 
the  beginning  of  the  contraction  and  its  maximum 
is  called  the  stage  of  increasing  energy ;  the  time  from 
this  maximum  to  that  of  the  full  re-extension  of  the 
muscle  is  that  of  the  stage  of  decreasing  energy.  The 
whole  duration  of  the  muscular  pulsation  from  the 
commencement  of  the  contraction  at  a  till  complete 
extension  is  again  reached  at  c,  is  from  about  one-tenth 
to  one-sixth  of  a  second. 


DETERMINATION    OF   TIME    BY    ELECTRICITY. 


57 


3.  In  a  similar  way  the  different  periods  in  muscnlar 
pulsation  may  be  measured  by  means  of  an  electric 
current.  In  order  to  understand  this  process,  let  us 
suppose  a  sudden  push  to  be  given  to  a  heavy  pendulum. 
The  pendulum  is  thus  caused  to  deflect  from  the 
vertical  position  proper  to  it  when 
quiescent,  the  angle  formed  by  its  de- 
flection depending  on  the  force  of  the 
push  which  operated  on  it.  Heavy 
pendulums  of  this  sort,  called  ballistic 
pendulums,  are  used  for  measuring 
the  speed  of  gun-shots.  A  magnetic 
needle  which  when  suspended  from  a 
thread  assumes  a  direction  from  north 
to  south,  may  be  regarded  as  a  pen- 
dulum in  which,  in  place  of  the  force 
of  gravitation,  the  magnetic  attraction 
of  the  earth  determines  its  position 
in  a  certain  direction.  If  a  sudden 
push  is  given  to  a  pendulum  of  this 
sort,  the  force  of  the  propulsion  may 
be  calculated  in  this  case  also  from 
the  degree  of  deflection.  If  a  con- 
tinuous electric  current  be  conducted 
to  a  magnetic  needle,  the  current 
being  parallel  to  the  needle,  the  latter 
deflects  and  assumes  a  position  at  an  angle  to  the  cur- 
rent, the  magnitude  of  this  angle  depending  on  the 
strength  of  the  current.  The  magnetic  needle  assumes 
a  new  position,  the  repelling  force  of  the  current  and  the 
mafjnetism  of  the  earth  counterbalancino"  each  other. 
If,  however,  the  current,  instead  of  acting  continuously, 
acts  only  for  a  short  time,  the  mngnetic  needle  suffers 
4 


Fig 


19.  Measi'he- 
mi;nt  of  small 
angles  of  deflec- 
TION WITH  JlIRKOll 
AND  LENS. 


58      PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

a  push  of  but  short  duration  and  makes  only  a  single 
vibration,  after  which  it  returns  to  the  position  proper  to 
it  when  at  rest.  The  degree  of  deflection  must  in  this 
case  be  proportionate  to  the  strength  of  the  current  and 
to  the  brevity  of  its  duration.  If,  therefore,  the  strength 
is  known  and  remains  constant,  the  time  occupied  by  the 
deflection  maybe  calculated  from  its  extent.  Such  de- 
flections are  generally  very  slight.  In  order,  therefore, 
to  measure  them  with  certainty,  an  apparatus  which  was 
first  applied  by  the  celebrated  mathematician  Gauss 
is  used.  A  small  mirror  o  being  connected  with  the 
magnet,  a  graduated  scale  s  s,  which  is  reflected  in 
the  mirror,  is  read  by  means  of  a  magnifying  glass.  If 
the  scale  is  placed  parallel  to  the  mirror  when  the 
magnet  is  at  rest,  and  the  magnifying  glass  is  arranged 
at  right  angles  to  the  direction  of  the  mirror  and  of  the 
scale,  it  is  evident  that  exactly  the  point  a  on  the 
scale  which  hes  over  the  centre  of  the  magnifying 
glass  will  be  seen  reflected  in  the  mirror.  As  soon  as 
the  magnet  with  the  mirror  attached  to  it  turns,  the 
reflection  of  a  different  point  on  the  fixed  scale,  the 
point  c,  is  seen  through  the  glass,  and  an  observer 
looking  at  the  mirror  through  the  lens  sees  the  scale 
apparently  move  in  the  same  direction  as  that  in 
which  the  mirror,  together  with  the  magnet,  turns. 
From  the  extent  of  this  change  of  position  the  angle 
which  the  magnet  describes  in  its  deflection  may  be 
calculated. 

4.  This  method,  by  which  the  duration  of  electric 
currents  may  be  measured  with  the  greatest  accuracy, 
must  now  be  applied  to  our  task  of  examining  the 
duration  of  a  muscle-pulsation.  For  this  purpose  we 
must   find    some    arrangement   by   which    an    electric 


MEASUREMENT   OF    PULSATION   BY   ELECTRICITY.       59 

current  is  closed  at  the  instant  at  -whicli  the  muscle  is 
irritated,  and  to  interrupt  this  current  at  the  instant  at 
which  the  contraction  of  the  muscle  begins. 

This  experiment  also  was  first  effected  by  Helmholtz. 
The  apparatus  used  for  the  purpose  is  shown  in  fig.  20, 
in  the  altered  form  used  by  du  Bois-Eeymond.  From 
a  fixed  stage  rises  a  column  to  which  a  strong  vice  for 
the  reception  of.  one  end  of  the  muscle  is  attached  in 
such  a  way  that  it  can  be  moved  upward  or  downward. 
The  lower  end  of  the  muscle  is  fixed  by  means  of  a 
connecting  piece  i  h  with  .a  lever  which  can  be  turned 
on  the  horizontal  axis  a  a'.  The  lever  is  prolonged 
below  into  a  short  rod  which,  passing  through  a  hole 
in  the  stage,  supports  at  its  foot  a  scale  plate  for 
weighting  the  muscle.  On  the  fore-end  of  the  lever 
are  two  screws  2^  and  q,  the  former  of  which  ends  below 
in  a  platinum  point  resting  upon  a  platinum  plate, 
while  the  latter  is  extended  into  a  point  of  copper- 
amalgam,  immersed  in  a  capsule  of  quicksilver.  The 
platinum  plate  and  the  capsule  of  quicksilver  are  iso- 
lated from  the  stage  and  from  each  other,  the  latter 
being  conduc^ively  connected  with  the  vice  k,  the  former 
with  /v/. 

If  the  current  which  is  to  act  on  the  swinging  mag- 
net is  inserted  between  h  and  k',  it  passes  through  the 
quicksilver  capsule,  through  the  portion  of  the  lever  be- 
tween 2^  and  q,  through  the  platinum  plate,  &c.,  as  long 
as  the  muscle  does  not  contract.  As  soon,  however,  as 
the  muscle  contracts,  it  interrupts  the  current  between 
p  and  the  platinum  plate.  If  the  apparatus  is  so  ar- 
ranged that  the  current  is  closed  at  the  moment  at 
which  any  irritant  affects  the  muscle,  then  this  current 
will  circulate  until  the  muscle,  in  contracting,  again 


60 


PHYSIOLOGY   OF   MUSCLES   AND   NERVES. 


Fig.  20.    ArrARATus  for  measitrtng  the  dui;atton  of  siuscle- 

CONTRACTIOX. 


MEASUREMENT   OF   PULSATION    BY   ELECTRICITY.       61 


interrupts  the  current.  This  period,  which  may  be  cal- 
culated by  the  method  described  in  the  last  paragraph, 
represents  exactly  that  which  elapses  from  the  moment 
at  which  the  irritant  affects  the  muscle  to  that  at  which 
contraction  begins. 

Yet  another  cu'cmnstance  must  be  taken  into  con- 
sideration, in  order  to  render  actual  measurements  pos- 
sible. The  muscle  contracts  on  being  irritated.  This 
contraction,  however,  lasts  only  a  very  few  parts  of  a 
second,  and  the  muscle  then  resumes  its  former  length. 
In  the  experiment  just 
described,  the  current 
interrupted  by  the  con- 
traction of  the  muscle 
would  soon  be  again 
completed,  and  the  mag- 
net would  undergo  a  new 
deflection  even  before 
the  first  vibration  was 
finished.  In  order  to 
obviate  this,  Helmholtz  ^'^'J^ 
employed  means  the  na- 
ture of  which  is  made 
intelligible  in  fig.  21.  This  figure  represents  the  end 
of  the  lever  of  the  apparatus  already  described,  together 
with  the  two  screws  p  and  q,  the  platinum  plate  and  the 
quicksilver  capsule ;  at  k  are  the  wires  connecting  the 
latter  with  the  vices.  The  quicksilver  in  the  capsule 
Hfj  can  be  raised  or  lowered  by  means  of  the  screw  s. 
If  the  level  of  the  quicksilver  is  raised  so  as  to  immerse 
the  point  q,  and  if  it  is  then  again  lowered,  the  quick- 
silver, by  adhesion,  remains  hanging  from  the  amalga- 
mated point,  and  is  by  this  means  drawn  out  in  the 


The  liXD  OF  the  lea'er  of 

THE  APPAUATfS  FOR  TIME  MEASITRE- 
:\1ENT,  TOGETHER  WITH  THE  QLKK- 
SILVER   CAPSULE. 


62 


PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 


form  of  a  thin  thread,  through  which  the  current  may 
pass.  When,  however,  the  muscle  shortens  the  quick- 
silver is  torn  away,  and  resumes  its  ordinary  convex 
surface ;   and  when,  on  the  extension  of  the  muscle, 


Fig.  22.    Diagram  ob^  experijient  for  the  electric  measurejmeht 

OE   TIJIE. 

the  lever  again  sinks,  though  the  point  p  again  rests  on 
the  platinum  plate,  yet  the  point  q  remains  separated 
from  the  quicksilver  by  an  intermediate  air-filled  space, 
and  the  current  remains  permanently  interrupted. 

It  still  has  to  be  explained  how  the  irritation  of  the 
muscle  and  the  closing  of  the  time-determining  current 


MEASUREMENT    OF    PULSATION    BY    ELECTRICITY.        63 

are  effected  exactly  at  the  moment  of  irritation.  A  clear 
idea  of  this  Tvill  be  gained  by  examining  fig.  22,  in  which 
the  arrangement  of  the  whole  experiment  is  diagram- 
matically  represented.  The  muscle  and  the  apparatus 
represented  in  fig.  20  are  again  shown.  The  muscle 
is  connected  with  the  secondary  coil  of  the  inductive 
apparatus  J' .  In  the  primary  coil  J  circulates  a  current 
from  the  chain  K.  This  current  passes  through  the 
platinum  plate  a,  and  through  the  platinum  point  a', 
a'  is  attached  to  a  lever  of  hard  wood,  a'  h\  and  is 
pressed  by  a  spring  against  the  platinum  plate  a.  At 
the  other  end  of  the  lever  is  the  platinum  plate  h\ 
which  is  connected  with  the  battery  B.  The  other  pole 
of  the  battery  is  in  connection  with  the  galvanometer 
g,  which  latter  is  itself  connected  with  the  quicksilver 
capsule  of  the  apparatus  represented  in  fig.  20.  Over, 
but  not  touching,  the  platinum  plate  h'  is  the  platinum 
point  6,  and  this  is  connected  with  the  platinum  plate  of 
the  same  apparatus  by  the  conductive  material  of  the 
key  s,  and  of  the  wire  h'.  On  pressing  down  the  key  s 
by  the  liandle,  the  platinum  point  h  comes  in  contact 
with  the  platinum  plate  6',  and  the  current  by  which 
the  time  is  to  be  measured  is  closed.  At  the  same 
time,  however,  the  end  a'  of  the  lever  a'  h'  is  raised, 
and  the  current  of  the  chain  K  is  interrupted.  This 
produces  an  inductive  current  in  the  coil  J'^  and  this 
irritates  the  muscle.  Irritation  is,  therefore,  induced 
exactly  at  the  moment  at  which  the  time-determining 
current  is  closed. 

As  soon  as  the  muscle  contracts,  it  interrupts  the 
time-determining  current.  This,  therefore,  lasts  from 
the  moment  of  irritation  to  that  at  which  the  pulsation 
commences.    In  this,  therefore,  we  measure  that  which 


64  PHYSIOLOGY   OF   MUSCLES   AND   NEKVES. 

we  called  the  stage  of  latent  irritation.  When,  how- 
ever, weights  are  placed  on  the  scale  of  the  apparatus 
(fig.  20),  the  resulting  deflections  of  the  magnetic  needle 
are  different,  and  are  greater  in  proportion  as  the  weight 
applied  is  heavier.  As  the  lever  connected  with  the 
muscle  rests  on,  and  is  supported  by,  the  plate  below 
it,  the  weights  placed  in  the  scale-plate  cannot  extend 
the  muscle ;  they  only  increase  the  pressure  of  the 
platinum  point  jp  on  the  underlying  platinum  plate. 
Before  the  muscle  can  contract  after  irritation,  the  ten- 
dency to  contraction  must  be  greater  than  this  pressure, 
or  than  the  tension  which  is  exercised  from  below  by 
the  weight  on  the  lever.  As  the  muscle  strives  to  draw 
up  the  lever,  while  the  weight,  on  the  other  hand,  draws 
it  downward,  the  greater  force  obtains  the  mastery.  It 
will  be  evident  from  what  has  been  said  that  the  muscle 
acquires  the  force  with  which  it  strives  to  contract,  not 
suddenly,  but  very  gradually.  At  the  moment  at  which 
this  contracting  force  becomes  slightly  greater  than  the 
weight  applied,  it  is  able  to  raise  the  lever,  and  in  so 
doing  to  interrupt  the  current  which  determines  the 
time.  If,  in  a  series  of  consecutive  experiments,  heavier 
weights  are  each  time  placed  in  the  scale  of  the  appa- 
ratus, and  if  the  deflections  of  the  magnetic  needle  re- 
sulting from  this  are  measured,  this  determines  the 
periods  in  which  the  muscle  attains  a  tendency  to  con- 
traction equivalent  to  the  weight.  We  will  call  this 
force  the  energy  of  the  muscle.  So  long  as  the  miiscle 
does  not  contract  at  all — that  is,  throughout  the  stage 
of  latent  irritation — its  energy  =  0.  From  the  periods 
which  we  find  as  the  result  of  the  application  of  in- 
creasing weights,  it  appears  that  this  energy  increases, 
at  first  rapidly  and  then  more  slowly,  reaching  its  maxi- 


BURDEN   AND    OVER-BURDEN.  65 

mum  in  about  one-tenth  of  a  second.  The  maximum 
having  been  reached,  the  muscle  is  unable  to  contract 
further.  The  energy  diminishes,  and  finally  disappears, 
the  muscle  retiuning  to  its  original  condition. 

5.  In  the  experiments  described  above,  weights  were 
connected  with  the  muscle  v>hich  the  latter  necessarily 
raised  as  soon  as  it  strove  to  contract;  but  these  weights 
did  not  act  upon  the  muscle  as  long  as  it  remained 
quiescent.  It  was,  therefore,  not  weighted  in  the  sense 
which  has  already  been  described ;  for  the  weights  at- 
tached were  unable  to  extend  the  muscle.  The  com- 
paratively slight  weight  of  the  lever  alone  extended  the 
muscle,  and  could  be  regarded  as  burden  in  the  ordinary 
sense.  In  order  to  distinguish  these  weights,  which 
are  without  effect  mitil  the  muscle  strives  to  contract 
from  weight  in  the  Ordinary  sense,  we  will  apply  the 
term  '  over-burden '  to  them.  The  burden  of  a  muscle 
may  be  great  or  small.  In  the  experiments  described 
above  it  was  equal  to  the  weight  of  the  lever.  Greater 
weightsmay  be  selected,  a  weight  being  placed  upon  the 
scale-plate  and  the  muscle  being  then  raised  by  means 
of  the  screw  at  the  top  of  the  apparatus,  so  long  as  the 
platinum  point  p  still  rests  on  the  platinum  plate.  The 
muscle  is  then  extended  by  the  weight  applied.  If 
additional  weight  is  added  to  that  already  on  the  scale- 
plate,  the  former  acts  as  burden,  the  latter  as  over- 
burden. When  a  muscle  thus  circumstanced  contracts, 
it  has  to  lift  both  weights.  Let  us  return  to  our  first 
series  of  experiments,  in  which  the  weight  =  0,  or  was 
at  least  very  small.  If  more  and  more  over-burden 
is  gradually  added,  it  is  evident  that  a  point  wiU  be 
reached  at  which  the  muscle  will  no  lonsfer  be  able  to 
lift  the  weight.     This  point   may  be   very  accurately 


66  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

determined  by  inserting  a  chain  and  an  electro-magnet 
between  the  vices  h  and  h' .  The  electric  current  then 
passes  through  the  platinum  point,  the  correspond- 
ing lever,  the  quicksilver  capsule,  and  the  coils  of  the 
electro-magnet.  The  latter  becomes  magnetic,  and  at- 
tracts an  armature.  As  soon,  however,  as  the  current 
is  interrupted  by  the  contraction  of  the  muscle,  the 
electro-magnet  sets  the  armature  free,  and  the  latter, 
striking  against  a  bell,  gives  a  signal  which  shows  that 
the  muscle  has  contracted.  In  this  way  even  very 
minute  contractions  of  the  muscle  are  recognised.  If 
the  weights  which  act  as  over-burden,  and  counter- 
balance the  tendency  to  contraction  in  the  muscle,  are 
gradually  increased,  a  limit  is  reached  at  which,  in  spite 
of  the  irritation  of  the  muscle,  the  current  of  the  electro- 
magnet is  no  longer  interrupted.  The  muscle  is  indeed 
irritated,  and  a  tendency  to  contraction  is  generated 
within  it ;  but  this  is  not  sufficiently  great  to  overcome 
the  weight  used  ;  and  the  muscle,  therefore,  remains 
uncontracted.  In  this  way  the  extent  to  which  the 
tendency  of  a  muscle  to  contract — or  its  energy,  as  we 
called  it,  can  increase — may  be  found.  This  extreme 
limit  of  its  energy  is  called  the  force  of  a  muscle.  It 
is  the  same  in  amount  as  that  which  we  theoretically 
inferred  (p.  48)  from  the  change  in  the  elasticity  of 
a  muscle  during  contraction.  Each  muscle  has  a  definite 
force  dependent  on  the  conditions  of  its  nourishment 
and  on  its  form.  On  comparing  the  muscles  of  the  same 
animal,  it  appears  that  the  force  is  dependent  in  no  way 
on  the  length  of  the  muscle-fibres,  but  on  the  number 
of  these  fibres,  or,  in  other  words,  on  the  diameter  of 
the  muscle ;  and  that  the  force  increases  in  exact  pro- 
portion with  the  diameter  of  the  muscle.     So  that  a 


MUSCLE-rORCE.  67 

muscle  of  double  thickness  therefore  possesses  double 
force.  It  is  usual,  therefore,  to  refer  the  force  to  units 
of  diameter  of  the  muscle,  by  dividing  the  force  by  the 
diameter  of  the  muscle,  and  thus  to  calculate  the  force 
of  a  muscle  of  1  square  centimetre  diameter.^  It  has 
been  found  that  in  the  muscles  of  the  frog  the  force, 
for  a  diameter  of  I  centimetre,  is  about  2*8  to  3  kilo- 
grammes ;  that  is  to  say,  a  muscle  of  1  centimetre  in 
diameter  can  attain  a  maximum  tendency  to  contraction 
■which  a  weight  of  3  kilogrammes  is  capable  of  resist- 
ing-. This  value  of  the  force  reduced  to  units  of  dia- 
meter  is  called  the  absolute  force  of  a  muscle. 

6.  An  attempt  has  been  made  to  determine  the  ab- 
solute muscular  force  in  the  case  of  man  also.  Edward 
Weber  first  tried  to  do  this  by  an  ingenious  method. 
The  muscles  of  the  calf  were  chosen  for  the  experiment. 
On  standing  upright  and  contracting  these,  the  heels, 
and  at  the  same  time  the  whole  body,  are  raised  from 
the  ground.  Grymnasts  call  this  balancing.  The  whole 
force  of  the  calf-muscles  of  both  legs  is  therefore  greater 
than  the  weight  of  the  body.  If  the  body  is  weighted, 
a  limit  is  reached  at  which  it  is  no  longer  possible  to 
balance.  The  total  weight  of  the  body  together  with 
that  of  all  the  weights  applied,  therefore,  equals  the 
force  of  the  muscles  of  the  calf;  but  in  calculating 
this,  however,  attention  must  be  paid  to  the  fact  that 
the  force  and  the  burden  do  not  act  on  the  same  lever. 


'  The  following  method,  adopted  by  Ed.  Weher,  is  used  to  de- 
termine the  diameter.  The  weight  of  the  muscle,  which  is  found 
by  the  use  of  scales,  is  multiplied  together  with  the  specitic  weight 
of  the  muscle-substance,  the  result  being  the  volume  of  the  muscle. 
The  length  of  the  muscle  is  then  measured,  and  the  volume  is 
divided  by  the  length,  which  gives  tl;e  diameter. 


68 


PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 


and  that  the  force — the  tension  exercised  bj  the  muscles 
of  the  calf — acts  obliquely  on  the  lever.  It  is  of  course 
impossible  to  determine  the  diameter  in  a  living  man ; 
it  must  be  observed  in  a  dead  body  of  about  the  same 
size  as  that  of  the  person  experimented  on. 

Henke  also  has  lately  determined  the  value  of  the 
absolute  force  of  human  muscle.  He  used  the  flexor 
muscles  of  the  forearm  (cf.  fig.  23)  to  determine  this. 
In  the  figure,  a  represents  the  upper  arm,  h  the  fore- 
arm—the former  being  in  a  ver- 
tical, the  latter  in  a  horizontal 
position ;  c  represents  the  muscles 
which  raise  or  bend  the  forearm. 
(There  are  in  reality  two  of  these 
muscles,  M.  biceps  and  M.  bra- 
chialis  internus).  Supposing  that 
the  muscles  are  stretched,  and 
weights  are  placed  on  the  hand 
till  the  muscles  are  no  longer  ca- 
pable of  raising  the  hand,  then, 
just  as  in  the  experiments  with 
the  muscles  of  frogs,  equipoise  is 
obtained  between  the  tendency  of  the  muscle  to  con- 
tract aud  the  weight  carried.  Care  must,  however,  be 
taken  that  the  muscles  act  on  a  long  lever  arm,  the 
weight  on  a  short  one,  and  the  weight  of  the  forearm 
itself  must  also  be  taken  into  consideration.  Due  at- 
tention being  given  to  all  these  circumstances,  and  to 
the  diameter  of  the  muscles  when  drawn  into  action, 
Henke  calculated  that  the  absolute  force  in  human 
muscle  is  equal  to  from  six  to  eight  kilogrammes.  Ex- 
perimenting in  a  similar  way  on  the  feet,  he  found 
somewhat  lower  figures  in  that  case.     Weber,  however, 


Fig.  23.    Diagram  of  the 
FLEXOu  :mlscles  of  the 

FOREARM. 


MEASUREMENT   OF   MUSCLE-FORCE    IN    MEN. 


69 


Fig.  24.    Dy.namomkter. 


in  his  results  as  regards  the  calf-muscles,  found  much 
lower  figures.  But  in  this  case,  errors  in  calculation 
evidently  occurred,  and  explain  the  diiference. 

To  determine  the  muscles  of  the  forearm  which 
bend  the  fingers,  a  dj'namometer,  as  represented  in  fig. 
24,  may  be  used.  The  strong  spring  handle  of  steel,  J., 
being  grasped  with  both 
hands,  is  pressed  together 
with  the  whole  strength. 
The  alteration  in  the 
curves  which  is  effected 
in  the  instrument  at  the 
points  d  and  d',  is  trans- 
mitted by  the  lever  a  b  a' 
to  the  index  c,  which  indi- 
cates in  kilogrammes  the  amount  of  force  exercised  on 
the  graduated  scale  B.  A  somewhat  elaborate  calcu- 
lation would  be  necessary  to  find  from  this  the  absolute 
force  of  the  muscles  employed.  If,  however,  the  force 
which  men  are  generally  able  to  exercise  with  their 
hands  is  known,  tTie  apparatus  may  be  conveniently  used 
to  detect  occasional  variations,  such  as  occur,  for  in- 
stance, at  the  commencement  of  lameness  and  other 
diseases  of  the  locomotive  apparatus.  The  dynamo- 
meter has,  therefore,  become  of  importance  in  the  in- 
vestigation of  diseases. 

7.  We  have  already  observed  that  a  muscle  dm-ing 
a  single  pulsation  attains  its  full  force,  not  at  once,  but 
only  gradually,  and  we  have  seen  the  way  in  which  the 
periods  necessary  for  attaining  the  different  values  of 
■  the  energy  may  be  determined  by  means  of  the  electric 
method  of  measuring  time.  If  the  muscle  contracts 
freely,  little  or  no  weight  being  attached,  it  exhibits 


70  PHYSIOLOGY   OF   MUSCLES    AND    NERVES. 

tliis  energy  during  each,  instant  in  tlie  form  of  increase 
in  speed  whicti  it  imparts  to  its  lower  end  and  to  the 
slight  weight  attached  to  the  latter.  We  may  now 
raise  the  question  as  to  the  amount  of  force  which  the 
muscle  when  it  has  already  accomplished  part,  say  one 
half,  of  its  contraction,  can  still  evolve.  Schwann,  who 
first  raised  the  question,  fastened  a  muscle  to  one  end 
of  the  beam  of  a  scale  and  attached  weights  to  the 
other  end,  but  supported  this  end  in  such  a  way  that 
the  muscle  was  not  extended.  He  was  thus  able  to 
determine  the  force  of  the  muscle  in  the  same  way  as 
was  described  above  with  the  apparatus  shown  in  fig.  20, 
which  depends  on  exactly  the  same  principle.  L.  Her- 
mann repeated  Schwann's  experiment  with  this  appa- 
ratus, which  is  more  convenient  for  the  purpose  now 
under  discussion.  The  unweighted,  or,  at  least,  "very 
slightly  weighted,  muscle  having  been  inserted  in  the 
apparatus  as  accurately  as  possible,  so  that  the  platinum 
point  2J  just  rests  on  the  plate,  the  muscular  force  is 
determined  in  the  way  described  above  (see  pp.  65,  67). 
The  ^ice  which  carries  the  muscle  is  then  lowered  to  a 
certain  definite  extent,  say  1  mm.  If  the  muscle  is 
then  irritated  it  can  become  shorter  by  1  mm.  before 
it  pulls  the  lever  A ;  if  it  becomes  yet  shorter  it  must 
raise  the  lever  with  the  weights  attached  to  it.  The 
weight  which  it  can  still  lift  after  it  has  become  shorter 
by  1  mm.  may  thus  be  found.  The  muscle-"\ice  is  then 
again  lowered — and  this  is  again  and  again  repeated. 
A  series  of  weight-values  is  thus  obtained  which  corre- 
spond with  the  force  of  the  muscle  dm'ing  the  different 
stages  of  its  contraction.  The  result  of  the  experiment 
is  to  show  that  the  force  of  the  muscle  decreases,  slowly 
at  the  commencement   of  contraction,  but  afterwards 


ALTEKATION   IN    MUSCLE-FORCE    DURING   CONTRACTION.  71 

more  rapidly.  The  muscle  having  contracted  as  far  as 
possible  without  any  weight,  it  can  naturally  no  longer 
raise  any  weight — its  whole  energy  is  expended. 

The  interest  of  this  experiment  lies  in  the  fact  that 
it  shows  in  a  different  way  that  which  we  have  already 
said  (p.  48)  as  to  change  in  elasticity  during  contraction. 
For  these  experiments  determine  the  weight  proper  to 
each  length  of  the  active  muscle,  so  that  we  can  also 
directly  deduce  from  these  the  curves  of  extension  of 
an  active  muscle,  which  we  had  previously  constructed 
only  theoretically.  The  agreement  of  this  deduction 
with  the  theory,  found  in  a  different  way,  is  an  impor- 
tant confirmation  of  the  views  which  we  have  developed 
as  to  the  bearing  of  the  conditions  of  elasticity  on  the 
labom"  accomplished  by  the  muscle. 


7'2  PUYSIOLOGY    OF   MUSCLES   AND   NERVES. 


CHAPTER  V. 

1.  Chemical  processes  within  the  muscle  ;  2.  Generation  of  warmth 
during  contraction ;  3.  Exhaustion  and  recovery;  4.  Source  of 
muscle-force ;  5.  Death  of  the  muscle ;  6.  Death-atiffening 
{Rigor  moi'tis), 

1.  The  relations  just  described  between  the  elasticity 
and  the  work  accomplished  by  the  muscle  have  led  us 
to  suppose  that  a  muscle  has,  as  it  were,  two  natural 
forms,  one  corresponding  to  its  condition  of  rest,  the 
other — a  shorter  form  —  corresponding  to  its  active  con- 
dition. Irritation  induces  the  muscle  to  pass  from  one 
form  into  the  other,  and  in  so  doing  it  contracts.  This 
is,  however,  rather  a  description  than  an  explanation 
of  the  fact  of  contraction.  As  the  muscle  on  contraction 
is  capable  of  raising  weight,  and  thus  of  accomplishing 
work,  it  is  necessary  to  inquire  how  this  labour  is 
effected.  According  to  the  law  of  the  conservation  of 
energy,  the  labour  so  accomplished  can  only  come  into 
existence  at  the  expense  of  some  other  energy.  Now, 
it  can  be  proved  that  chemical  processes  proceed  within 
the  muscle  during  muscular  contraction,  while  others, 
which  proceed  even  in  the  quiescent  muscle,  are  in- 
creased in  degree  during  this  same  contraction.  The 
mechanical  work  must,  therefore,  be  accomplished  at 
the  expense  of  these  chemical  processes ;  and  it  could 


CHEMICAL   PROCESSES   IN   MUSCLE.  73 

be  proved  that  the  amount  of  work  accomplished  corre- 
sponds exactly  with  these  chemical  changes. 

It  is  easy  to  show  that  chemical  processes  occur 
within  the  muscle ;  but  it  is  not  so  easy  to  determine 
these  quantitatively,  so  that  we  are  as  yet  imable  to 
solve  the  question  raised.  Helmholtz  long  ago  pointed 
out  the  fact  that  during  muscular  contraction  such  con- 
stituents of  the  muscle  as  are  soluble  in  water  decrease, 
while  such  as  are  soluble  in  alcohol  increase.  E.  du  Bois- 
Eeymond  showed  that  an  acid — probably  a  lactic  acid 
{FleischmUchsdiire) — is  generated  in  the  muscle  duriug 
its  activity.  Quiescent  muscles  also  contain  a  certain 
amount  of  a  starch-Hke  matter  called  glycogen ;  and,  as 
Nasse  and  Weiss  have  shown,  part  of  the  glycogen  is  used 
up  during  the  activity  of  the  muscle,  and  is  transformed 
into  sugar  and  lactic  acid.  Finally,  it  can  be  shown 
that  carbonic  acid  is  generated  in  the  muscle  during  its 
contraction.  All  these  chemical  changes  are  capable  of 
producing  warmth  and  work.  In  determining  whether 
the  whole  amount  of  work  accomplished  is  referable  to 
this  source,  yet  another  special  difficulty  exists  in  the 
fact  that,  as  in  other  machines,  warmth  is  also  produced 
as  well  as  mechanical  work.  A  muscle  certainly  grows 
warmer  during  its  contraction,  as  Beclard  and,  with  yet 
greater  certainty,  Helmholtz  have  shown.  With  suitable 
apparatus  it  is  possible  to  indicate  an  increase  in  the 
warmth  of  a  muscle  even  during  a  single  contraction. 

Our  knowledge  of  the  chemical  constituents  of 
muscle  is  yet  very  incomplete.  Not  only  is  chemistry 
as  yet  unprovided  with  adequate  means  of  examining 
albuminous  bodies,  which  are  the  chief  constituents  of 
muscles,  but  a  special  difficulty  also  exists  in  the  great 
tendency  to  change  in  the  constituent  matter  of  living 


74  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

muscle.  The  methods  .usually  employed  in  chemistry 
for  the  separation  and  isolation  of  different  substances 
are  of  no  avail  in  this  case,  since  they  essentially  alter 
the  nature  of  the  muscle.  We  must,  therefore,  be  satis- 
fied to  assume  as  certain  only  that  various  albuminous 
bodies  occur  in  the  muscle,  one  of  which,  called  myosin, 
appears  to  be  peculiar  to  muscle,  and  of  which  others 
are  the  non-nitrogenous  bodies  glycogen  and  inosit, 
together  with  a  certain  amount  of  fat  and  a  number  of 
salts.'  It  appears  somewhat  doubtful  whether  lactic 
acid,  which  is  always  present  in  the  muscle,  if  but  in 
small 'quantities,  is  to  be  regarded  as  a  normal  con- 
stituent of  muscle  substance,  or  if  it  is  not  rather  a 
product  of  decomposition.  The  same  may  be  said  of 
the  gaseous  carbonic  acid  which,  like  the-  lactic  acid,  is 
probably  only  formed  during  the  activity  of  the  muscle, 
and  also  of  the  nitrogenous  bodies,  such  as  creatin,  which 
are  present  in  small  quantities  in  muscle,  and  which 
must  probably  also  be  regarded  only  as  the  products  of 
the  dissolution  of  the  albuminous  bodies. 

2.  The  only  conclusion  to  be  drawn  from  this  frag- 
mentary information  is  that  part  of  the  muscle-substance 
unites  during  the  activity  of  the  muscle  with  oxygen, 
forming,  partly  carbonic  acid,  partly  less  highly  oxidised 
products.  That  warmth  is  generated  during  these  pro- 
jesses  of  oxidation,  as  we  have  above  stated,  is  not  sur- 
prising. To  show  this  generation  of  warmth,  Helmholtz 
employed  the  thermo-electric  method.  An  electric  cur- 
rent rises  in  a  circle  composed  of  two  different  metals,  e.g. 
copper  and  iron,  as  soon  as  both  points  of  contact — the 
points  where  the  metals  meet  or  are  soldered  together' 
— acquire  unequal  temperatures.  The  strength  of  this 
current  is  proportionate  to  the  differeDce  in  temperature, 


GENERATION   OF    WARMTH    DUEI^^G    CONTRACTION.      ID 

and  thus,  from  the  strength  of  the  current,  it  is  possible 
to  determine  the  temperature  of  one  point  of  contact 
if  that  of  the  other  is  known.  In  our  case,  in  which  it 
is  not  necessary  to  determine  absolute  temperatures, 
but  only  to  show  an  increase  in  warmth,  the  method  is 
more  simple.  It  is  only  necessary  to  provide  that  the 
two  points  of  contact  have  the  same  temperature  at 
first,  a  cond,ition  which  can  be  recognised  by  the  absence 
of  any  current,  and  the  additional  degree  of  warmth  ac- 
quired can  then  be  directly  calculated  from  the  strength 
of  the  current  which  is  afterwards  generated. 

Helmholtz  performed  the  experiment  by  placing 
the  two  thighs  of  a  frog  which  had  been  recently  killed 
in  a  closed  case,  after  he  had  so  arranged  the  metals 
w^iich  were  to  determine  the  warmth  that  one  point  of 
contact  was  inserted  in  the  muscles  of  one  thigh,  the 
other  in  those  of  the  other  He  then  waited  till  the 
temperatures  of  both  thighs  became  equal,  so  that, 
though  the  metals  were  connected  with  a  sensitive  mul- 
tiplier, no  current  was  apparent.  The  muscles  of  one 
thigh  were  thrown  into  strong  tetanus  by  introducing 
a  suitable  inductive  current,  while  those  of  the  other 
thigh  remained  at  rest.  The  contracted  muscles  then 
became  warmer  and  imparted  their  warmth  to  the 
soldered  metals  embedded  in  them ;  the  result  was  an 
electric  current  the  strength  of  which  was  measured. 
The  increase  in  the  warmth  of  the  muscle,  thus  de- 
termined, was  about  -15  of  a  degree.  This  warmth 
may  seem  slight,  but  it  must  be  remembered  that  but 
a  small  mass  of  muscie  was  treated,  and  that  this 
necessarily  lost  a  considerable  part  of  the  w^armth  gene- 
rated within  it  by  radiation  and  by  imparting  it  to  the 
surroundino:  substances. 


76  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

In  order  to  form  some  conception  of  the  amount  of 
warmth  thus  generated,  we  will  assume  that  the  specific 
warmth  of  muscle  is  the  same  as  that  of  water.  As  the 
greater  part  of  muscle  consists  of  water,'  this  assumption 
cannot  he  far  ■wTong.  By  the  specific  warmth  of  a  sub- 
stance is  meant  that  amount  of  warmth  which  is  neces- 
sary to  warm  one  gramme  of  the  substance  exactly  one 
degree,  the  amount  necessary  in  the  case  of  water  being 
regarded  as  the  unit.  Therefore  about  one  unit  of 
warmth  is  requisite  to  warm  one  gramme  of  muscle 
substance  one  degree.  According  to  our  assumption,  in 
each  gramme  of  muscle  substance  at  least  "15  of  a  unit 
of  warmth  is  generated.  Now  it  is  known  that  each 
unit  of  warmth  is  equivalent  to  424  units  of  work,  that 
is  to  say,  when  warmth  is  transformed  into  mechanical 
work,  424  grammes  can  be  raised  one  metre  by  one 
unit  of  warmth.  If,  therefore,  no  warmth  were  set  free 
from  the  muscle  during  tetanus,  but  if  it  were  trans- 
formed into  work,  each  gramme  of  muscle  substance 
would  be  able  to  raise  424-^0*15  gramme  to  the  height 
of  one  metre.  This  amount,  therefore,  represents  the 
minimum  of  that  which  is  accomplished  as  '  internal 
work '  in  the  muscle  during  tetanus. 

By  soldering  rods  or  strips  of  two  metals  alternately 
on  to  each  other  so  that  aR  the  points  soldered  are 
aiTanged  in  two  planes,  differences  in  temperature  much 
more  minvite  than  those  which  occur  during  tetanus 
may  be  measured.  Such  an  apparatus  is  called  a  thermo- 
pile.    Heidenhain  had  one  of  these  made  of  rods  of 

'  According  to  a  recent  statement  of  Dr.  Adamkiewicz,  the  spe- 
cific warmth  of  muscle  is  even  greater  than  that  of  water,  though  it 
had  previously  been  assumed  that  the  specific  warmth  of  water  is 
greater  than  that  of  any  other  known  substance,  with  the  excep- 
tion of  hydrogen. 


GENERATION  OF  WAEMTH  DURING  CONTRACTION.   77 

antimony  and  bismuth,  and  having  covered  the  surface 
of  each  of  the  ends  with  a  muscle  from  the  lower  leg 
of  a  frog,  he  waited  until  both  had  assumed  an  equal 
temperature.  He  then  by  irritation  induced  activity 
in  one  muscle,  and  owing  to  the  sensitiveness  of  the 
apparatus  he  was  not  only  able  to  determine  the  warmth 
arising  during  a  single  pulsation,  but  even  to  indicate 
differences  in  this  according  to  the  circumstances 
(burden,  &c)  under  which  the  pulsation  occrured. 

The  law  of  the  conservation  of  energy  would  lead 
us  to  expect  that  in  cases  in  which  the  muscle  ac- 
complished a  greater  amount  of  mechanical  work,  the 
production  of  warmth  would  be  less,  and  vice  versa. 
When  weights  are  applied,  as  burden,  to  the  muscle, 
the  labour  performed  increases,  as  we  found,  up  to  a 
certain  point  with  every  increase  in  weight.  The 
generation  of  warmth  should  accordingly  decrease  in 
this  case.  This  was  not,  however,  the  case  in  the 
experiments  made  by  Heidenhain.  As  we  cannot  sup- 
pose that  the  law  of  the  conservation  of  energy,'  whic^h 
is  elsewhere  throughout  nature  universally  valid,  is 
invalid  as  regards  muscle,  we  can  only  suppose  that 
the  number  of  chemical  modifications  occurring  at  each 
muscular  pulsation  is  not  always  the  same,  but  that 
when  greater  weight  is  applied  a  larger  amount  of 
substances  are  consumed  in  the  muscle,  so  that  both 
the  production  of  warmth  and  the  work  accomplished 
may,  though  the  irritant  remains  the  same,  diflfer 
according  to  the  degree  of  tension  of  the  muscle.  On 
the  other  hand,  it  is  quite  in  accordance  with  the  law 
of  the  conservation  of  energy  that  the  muscle  generates 

'  On  this  law  sec  the  admirable  work  of  Ealfoiir  Stewart  (Inter- 
national Scientific  Series,  vol.  vi.). 


78  THYSIOLOGY    OF   MUSCLES    AND    NERVES. 

the  greatest  amount  of  warmtli  during  tetanus,  d\n'ing 
wMcIl  no  apparent  labour  is  accomplished.  The  whole 
internal  work  of  the  muscle  is  in  this  case  transformed 
into  warmth,  thus  raising  the  temperature  of  the  muscle- 
substance  ;  and  the  amount  of  this  warmth  may,  as  we 
have  seen,  be  at  least  approximately  measured  and 
calculated. 

3.  One  result  of  the  chemical  changes  which  occur 
Avithin  the  muscle  dm-ing  its  activity,  is  naturally 
that  part  of  the  constituent  matter  of  the  muscle  is 
expended,  other  matter  being  deposited  in  its  place. 
As  long  as  the  muscle  remains  uninjured  within  the 
body  of  the  animal,  part  of  the  matter  thus  formed  is 
carried  away,  and  fresh  nutritive  matter  is  brought  to 
replace  the  expended  material.  The  products  which 
arise  by  decomposition  during  the  activity  of  the 
muscle  may  therefore  be  indicated  in  the  blood  of  the 
animal,  and  from  the  blood  they  are  removed  from  out 
of  the  body  by  special  excretory  organs.  Accordingly 
we  find  that  the  amount  of  carbonic  acid  excreted  is 
considerably  increased  by  muscular  labour,  and  that 
the  other  products  of  muscular  decomposition,  such  as 
creatin  and  the  urea  arising  from  the  latter,  lactic  acid, 
&c.,  reappear  in  the  m-ine.  The  more  abundantly 
the  blood-current  flows  through  the  muscles,  the  more 
quickly  are  the  products  of  decomposition  removed 
from  the  muscle.  This  is  of  course  possible  only  in  a 
very  inferior  degree  when  the  muscle  has  been  cut  out 
from  the  body.  This  is  the  reason  why  an  extracted 
muscle  retains  its  power  of  activity  for  but  a  very  short 
time.  If,  for  instance,  such  a  muscle  is  continuously 
tetanised,  it  will  be  found  that  the  contraction,  though 
it  is  at  first  very  considerable,  very  soon  decreases  and 


EXHAUSTION?   AND   EECOVERY.  79 

finally  entirely  ceases.  The  muscle  is  then  said  to  be 
exhausted.  But  if  it  is  allowed  to  rest  it  recovers 
itself  so  that  it  can  again  be  induced  to  contract.  This 
recovery  is,  however,  never  complete,  and  with  each 
repetition  of  the  experiment  it  becomes  more  defec- 
tive, the  intervals  requisite  for  recovery  becoming 
continually  longer,  and  the  muscle  finally  remaining 
incapable  of  further  contraction.  If  the  muscle  is  not 
tetanised,  but  distinct  pulsations  are  induced  in  it  by 
separate  irritants,  it  retains  its  power  of  activity  for  a 
very  long  time.  From  this  it  may  be  inferred  that  a 
portion  of  the  products  of  decomposition  perhaps  re- 
form ;  or  it  may  be  assumed  that  the  muscle  contains  a 
large  amount  of  matter  capable  of  disintegration,  but 
that  this  is  capable  of  only  gradual  decomposition.  So 
long  as  the  blood  continues  to  flow  through  the  muscle, 
the  products  of  decomposition  are,  as  we  have  seen, 
soon  carried  away ;  but  as  exhaustion  occurs  in  this  case 
also,  we  must  draw  the  same  conclusion,  that  the  de- 
composable matter  present  can  undergo  decomposition 
only  gradually,  and  that  therefore  in  this  case  also 
intervals  must  necessarily  occur  between  the  separate 
exercises  of  activity.  A  muscle  while  undisturbed  within 
the  organism  essentially  differs  from  one  that  has  been 
extracted  in  that  in  the  former  the  expended  material 
can  be  fully  replaced.  Accordingly,  it  is  not  only  capable 
of  again  becoming  active  after  an  interval  of  rest,  but, 
provided  that  the  matter  added  exceeds  that  which  was 
expended,  it  is  afterward  capable  of  performing  more 
work  than  it  was  previously.  To  this  is  due  the  fact 
that  the  strength  of  muscle  is  increased  by  a  proper 
alternation  of  rest  and  activity. 

4.  We  have  now  to  discover  which  of  the  substances 


80  PHYSIOLOGY    OF   MUSCLES    AND    NEEVES. 

within  the  muscle  are  expended  during  its  activity. 
As  muscle  consists  principally  of  albuminous  bodies,  it 
has  been  assumed  that  it  is  to  the  decomposition  of 
these  that  the  labour  accomplished  is  due.  We  have, 
however,  seen  that  non-nitrogenous  bodies,  such  as 
glycogen  and  muscle-sugar,  are  also  contained  in  the 
muscle,  and  that  lactic  acid,  which  must  originate 
from  the  latter,  is  formed  during  the  active  state. 
Although  it  is  impossible  to  determine  the  products  of 
decomposition  within  a  single  muscle,  yet  this  may  be 
done  in  the  case  of  the  whole  mass  of  the  muscles  of 
the  body  during  an  activity  of  long  continuance ;  for 
the  products  of  decomposition  finally  pass  into  the  ex- 
cretions, and  it  is  evident  that  the  whole  amount  of 
addition  to  the  excretions  may  be  regarded  as  a 
measure  of  the  decomposition  in  the  active  muscles. 
The  nitrogenous  constituents  of  muscle  are  almost 
without  exception  excreted  in  the  form  of  urea  with 
the  urine.  At  least  the  amount  of  nitrogen  contained 
in  the  other  excretory  products  is  so  very  small  that  it 
may  safely  be  disregarded.  Now,  the  amoxmt  of  urea 
contained  in  the  urine  may  be  determined  with  very 
great  accuracy.  Even  when  the  body  is  in  a  state  of 
complete  rest — though  even  then  a  considerable  amount 
of  work  is  performed  in  the  body,  in  the  action  of  the 
heart  and  of  the  respiratory  muscles — the  excretion  of 
urea  depends  entirely  on  the  amount  of  nitrogen  intro- 
duced in  food.  If  entirely  non-nitrogenous  food  is 
taken,  then  the  excretion  of  urea  decreases  to  a  definite 
point,  at  which  it  remains  constant  for  some  time.  If 
a  larger  amount  of  work  is  performed,  a  slight  increase 
in  the  excretion  of  urea  in  fact  usually  occurs.  The 
a.mount  of  albuminous  matter  which  must  be  modified 


SOuRCE   OF  MUSCLE-FORCE.  81 

within  the  body  in  order  to  afiford  this  increase  in  the 
amount  of  urea  excreted  may  be  calculated.  Now,  the 
equivalent  in  warmth  of  albuminous  bodies  is  known ; 
that  is,  the  amount  of  warmth  produced  by  the  com- 
bustion of  a  definite  weight  of  albuminous  matter  is 
known.  And,  as  the  mechanical  equivalent  of  warmth 
is  also  known,  the  amount  of  work  which  could  be 
produced  by  these  albuminous  bodies  under  favourable 
circumstances  may,  therefore,  also  be  calculated.  "When 
this  value  in  work  is  compared  with  the  amount  of 
work  really  accomplished,  the  figures  found  are  always 
far  too  low.  From  this  it  may  safely  be  inferred  that 
the  albuminous  matter  which  undergoes  combustion 
within  the  body  is  not  capable  of  affording  the  work 
which  is  performed,  and  we  must  rather  assume  that 
other  substances  also  undergo  combustion,  and  con- 
tribute to  the  labour  performed,  contribute  indeed  even 
the  greater  part  of  such  labour.  If,  on  the  other  hand, 
the  amount  of  carbonic  acid  excreted  by  a  man  during 
rest  is  compared  with  that  excreted  during  greater 
labour,  the  increase  is  foimd  to  be  very  great  indeed, 
and  on  calculating  the  amount  of  labour  which  should 
result  from  the  combustion  of  a  corresj)onding  mass  of 
carbon,  the  amount  found  corresponds  nearly  enough 
with  that  of  the  work  really  performed. 

This  experiment,  therefore,  shows  that  the  muscles 
generate  their  work  not  so  much  at  the  expense  of 
albuminous  bodies  as  by  the  combustion  of  non-nitro- 
genous matter.  The  addition  of  matter  reqmred  by  the 
body  if  it  is  to  remain  in  a  condition  capable  of  labour 
must,  therefore,  be  regulated  accordingly.  Hence  fol- 
'  lows  the  conclusion,  of  the  greatest  importance  with 
reference  to  the  question  of  diet,  that  men  who  have 


82  PHYSIOLOGY   OF   MUSCLES   AND  NERVES. 

to  perform  a  great  amount  of  labom*  require  food 
abounding  in  carbon.  The  opposite  was  formerly  as- 
sumed, the  view  being  founded  on  the  fact  that  English 
labourers,  who  are,  as  a  rule,  more  capable  of  work 
than  French  peasants,  eat  more  meat,  which  is  a  highly 
nitrogenous  substance.  It  used  also  to  be  pointed  out 
that  the  larger  beasts  of  prey,  which  feed  exclusively 
on  flesh,  are  remarkable  for  their  great  muscular  power. 
Neither  instance  really  proves  the  conclusion  which  it 
was  intended  should  be  drawn  from  it.  In  the  first 
place,  as  regards  English  labourers,  more  accurate  ob- 
servation of  the  food  usually  consumed  by  them  has 
shown  that,  in  addition  to  meat,  very  considerable 
quantities  of  food  abounding  in  carbon,  such  as  bread, 
potatoes,  rice,  and  so  on,  are  taken.  As  regards  the 
beasts  of  prey,  it  is  impossible  to  deny  that  they  are 
capable  of  very  great  labour;  but  in  this  case,  also, 
closer  observation  shows  that  the  whole  amount  of 
work  accomplished  by  them  is,  at  any  rate,  very  small 
when  compared  with  the  constant  work  of  a  draught 
horse  or  ox. 

The  relation  of  the  food  to  the  work  performed  by 
the  muscles  must  evidently  be  regarded  as  similar  to 
the  relation  borne  by  the  fuel  consumed  by  an  engine 
boiler  to  the  work  performed  by  a  steam-engine.  Every- 
one knows  that  coal  is  burned  under  the  boiler,  and 
that  this  is  finally  transformed  into  work  by  the  me- 
chanism of  the  machine.  The  same  work  might  be 
produced  by  the  combustion  of  nitrogenous  matter; 
but  it  would  be  necessary  to  use  considerably  greater 
quantities.  But  the  machine  called  muscle  cannot  be 
driven  by  pure  carbon ;  under  the  conditions  presented' 
by  the  organism  pure  carbon  cannot  be  applied  to  the 


SOURCE    OF   MUSCLE-FORCE.  83 

production  of  work,  as  it  cannot  be  digested,  and,  owing 
to  the  low  temperature  of  the  body,  cannot  be  oxidised. 
But  combinations  abounding  in  carbon,  such  as  are  at 
hand  in  the  carbon  hydrates  (starch,  sugar,  &c.)  and  in 
fats,  are  fitted  for  the  purpose,  and  a  given  weight  of 
these  affords  a  considerably  greater  amount  of  work 
than  can  an  equal  weight  of  nitrogenous  albumens. 
If,  therefore,  the  muscle  is  capable,  by  the  combustion 
of  the  non -nitrogenous  bodies  which  it  contains,  of  ac- 
complishing labour,  it  is  evident  that  this  relation  is 
similar  to  that  in  the  case  of  the  steam-engine,  in  which 
the  work  is  accomplished  by  the  combustion  of  carbon. 
It  Las  been  objected  that  the  amount  of  non-nitro- 
genous substance  within  the  muscle  is  very  small,  but 
the  objection  is  scarcely  tenable.  If  a  whole  steam- 
engine  with  its  boiler  and  the  coal  in  the  furnace  could 
be  subjected  to  a  chemical  analysis,  the  percentage  of 
coal  in  the  whole  mass  would  of  course  be  found  to  be 
very  small.  But  it  is  not  by  the  amount  of  coal  present 
at  any  given  moment  that  the  work  is  performed,  but  by 
the  whole  amount  which  in  the  course  of  a  considerable 
time  is  added  little  by  little  by  the  stoker.  In  the 
case  of  muscle  the  blood  acts  the  part  of  the  stoker. 
It  continually  adds  matter  to  the  muscle,,  and  the 
products  of  combustion  resulting  from  labour  escape 
from  the  muscle,  just  as  the  carbonic  acid  does  from 
the  chimney  of  the  steam-engine.  It  is  evident  that 
the  amount  of  carbon  consumed  by  a  steam-engine 
might  be  accurately  determined  by  collecting  and 
analysing  the  carbonic  acid  which  escapes  from  the 
chimney.  We  proceed  in  exactly  the  same  way  in  the 
case  of  the  muscle.  The  lungs  represent  the  chimney ; 
the  carbonic  acid  escaping  from  these  may  be  collected, 


84  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

and  from  this  the  amount  of  carbon  which  must  be  con- 
sumed may  be  calculated.  AYhatever  does  not  escape 
in  the  form  of  gas  during  combustion  remains  behind 
as  ash.  The  ash  of  the  fire  of  the  steam-engine  is 
represented  by  the  urea  and  other  matter  which  passes 
from  the  muscles  into  the  urine.  The  whole  amount  of 
both  must  correspond  exactly  with  the  whole  amount 
of  the  products  resulting  from  combustion  within  the 
muscle. 

Although  the  small  amount  of  the  non-nitrogenous 
substances  present  in  the  muscle  does  not,  therefore, 
prevent  us  from  regarding  them  as  the  main  source  of 
muscular  labour,  yet  in  one  point  the  machine  called 
muscle  differs  from  the  steam-engine,  which  it  other- 
wise so  strikingly  rcisembles.  We  found  that  the  ex- 
cretion of  urea  undergoes  an  increase,  though  this  may 
not  be  very  great,  when  the  muscular  labour  is  in- 
creased. It  is,  therefore,  evident  that  there  must  be  a 
greater  destruction  of  the  chief  constituents  of  muscle- 
substance,  of  the  tissue  of  which  muscle  is  mainly 
formed,  and  which  may  be  compared  to  the  metallic 
parts  of  the  steam-engine.  Even  in  the  latter  a  waste 
of  the  metalHc  parts  occurs ;  but  this  is  comparatively 
very  small  in  degree.  The  muscular  machine  is  not 
constructed  of  such  durable  material ;  during  its  ac- 
tivity it,  therefore,  continually  wastes  a  comparatively 
considerable  amount  of  its  own  substance.  As  the 
matter  leaves  the  body  in  a  more  highly  oxidised  form 
than  it  had  when  it  was  present  in  the  muscle,  warmth 
and  work  must  also  be  freed  during  this  partial  com- 
bustion of  the  material  of  the  machine.  The  muscle- 
machine  works,  therefore,  partly  at  the  expense  of  its 
own  form-element ;  and,  if  it  is  to  work  continuously,  not 


SOURCE   OF   MUSCLE-FOKCE.  85 

only  must  the  main  fuel,  but  also  matter  to  replace  the 
form-element  must  be  constantly  added.  The  more 
closely  the  composition  of  the  food  consumed  corre- 
sponds with  the  material  expended,  the  more  complete 
will  be  the  replacement  which  can  occm-.  The  expen- 
diture of  non-nitrogenous  substance  is,  as  we  found, 
comparatively  great,  so  that  it  would  be  entirely  wrong 
to  try  to  supply  the  loss  merely  with  nitrogenous  matter. 
All  experience  in  the  nourishment  of  labouring  men 
and  animals  fully  confirms  this.  The  addition  of  nitro- 
genous matter  is  necessary,  to  keep  the  muscles  in  good 
condition ;  but  a  yet  more  abundant  addition  of  carbon 
compounds,  such  as  are  afforded  by  the  non-nitrogenous 
food  materials,  is  required,  in  order  to  supply  the  neces- 
sary amount  of  the  chief  producer  of  labom*.  The 
wood-cutters  of  the  Tyrol,  who  work  exceedingly  hard 
and  with  great  expenditure  of  strength,  accordingly  con- 
sume an  immense  amount  of  food  abounding  in  carbon 
in  addition  to  a  certain  quantity  of  nitrogenous  matter. 
They  live  almost  exclusively  on  flour  and  butter.  Only 
on  one  day  in  the  week,  Sunday,  do  they  eat  meat  and 
drink  beer.  For  six  days  they  are  limited  to  whatever 
they  carry  into  the  forests  with  them.  The  nature  of 
the  food  may,  therefore,  be  very  accm-ately  regulated 
in  this  case.  Their  power  of  enduring  very  great  toil 
is  principally  due  to  the  large  amount  of  fat  contained 
in  their  daily  food.  Chamois  hunters  and  other  moun- 
taineers take  chiefly  bacon  and  sugar  by  way  of  pro- 
vision on  their  laborious  expeditions.  Experience  has 
taught  them  that  these  highly  carboniferous  com- 
pounds are  especially  suited  to  enable  them  to  accom- 
plish great  labour.  Sugar  is  especially  suitable  for 
the  purpose,    because,  being  very  readily   soluble,  it 


86  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

passes  rapidly  into  the  blood,  and  is,  therefore,  espe- 
cially capable  of  rapidly  replacing  the  expended  forces. 
It  is  not  suitable  for  a  sole  or  main  food  material  durins' 
long  periods,  because  when  a  great  quantity  of  sugar 
is  introduced  into  the  stomach  it  is  transformed  into 
lactic  acid  and  the  digestion  is  injiured. 

5.  When  muscles  have  lain  by  for  some  time  after 
their  extraction  from  the  body,  a  change  occurs  in  them 
which  deprives  them  of  their  capacity  for  contracting 
when  irritated.  This  change  intervenes  yet  more 
rapidly  when  they  are  induced  to  pass  into  a  state  of 
activity  by  many  repeated  irritations.  The  time  neces- 
sary for  the  intervention  of  this  change  varies  much, 
and  depends  chiefly  on  the  nature  of  the  animal  and  on 
the  temperatm'e.  The  muscles  of  mammals  in  a  tem- 
perature such  as  that  of  an  ordinary  room  lose  their 
power  of  contraction  in  as  little  as  from  twenty  to 
thirty  minutes ;  the  muscles  of  frogs  do  not  lose  this 
power  for  several  hours,  and  some  from  the  calf-muscle  of 
a  frog  have  been  observed  to  pulsate  even  for  forty-eight 
hours  in  the  temperature  of  an  ordinary  room.  At  a 
temperature  of  from  0°  to  1°  C.  the  same  muscle  may 
retain  its  power  of  contraction  even  for  eight  days.  On 
the  other  hand,  in  a  temperature  of,  or  above,  45°,  the 
contractile  power  is  lost  in  a  few  minutes.  Exactly 
the  same  happens  in  muscles  yet  remaining  within  the 
body  of  the  animal  if  the  blood-current  ceases  to  pass 
through  the  body,  either  because  of  the  death  of  the 
animal,  or  in  consequence  of  the  local  application  of 
ligatures  to  the  vessels.  This  loss  of  contractile  power 
is  spoken  of  as  the  death  of  the  muscle.  Muscular 
death  does  not,  therefore,  correspond  in  time  with  the 
general  death  of  the  whole  animal,  but  it  follows  this 


DEATH    OF   THE   MUSCLE.  87 

general  death  at  a  period  varying  from  thirty  minutes 
to  several  hours. 

6.  On  looking  at  the  dead  muscle  of  a  frog  it  will  be 
noticed  that  its  appearance  differs  essentially  from  that 
of  a  fresh  muscle.  It  does  not  appear  so  transparent,  is 
much  duller  and  whiter  in  colour ;  at  the  same  time  it 
feels  harder,  less  elastic,  but  is  capable  of  greater  ex- 
tension, and,  iinally,  it  is  tender  and  easily  torn  apart, 
the  more  so  the  further  the  change  has  proceeded.  Ex- 
actly similar  changes  affect  the  muscles  of  a  dead  body. 
This  is  called  the  death-stiffening  (rigor  mortis).  E.  du 
Bois-Keymond  showed  that  on  the  occurrence  of  this 
death-stiffening  the  original  alkaline  or  neutral  reaction 
gives  place  to  an  acid  reaction.  This  is  probably  due  to 
the  transformation  of  the  neutral  glycogen  and  inosit 
into  lactic  acid,  which  with  the  alkalis  present  forms 
acid-reacting  salts.  This  change  is  the  cause  of  the 
fact  that  butcher's  meat,  which  remains  hard  and  tough 
if  it  is  cooked  directly  after  death,  becomes  gi-adually 
more  tender.  If  the  meat  is  allowed  to  lie  for  a  time 
after  death,  the  death-stiffening  again  relaxes,  the  sepa- 
rate bundles  of  fibres  no  longer  adhere  so  firmly  to 
each  other ;  and  when  in  this  condition  the  meat  is 
better  adapted  for  preparation  as  food,  because  it  is 
tender  and  may  be  more  easily  chewed,  and  because 
it  offers  less  resistance  to  the  digestive  juices. 

The  death-stiffening  in  its  chemical  nature,  there- 
fore, bears  a  certain  resemblance  to  the  changes  which 
occur  during  the  activity  of  the  muscle.  In  the  latter 
case  also  an  acid  is  formed,  which  is,  however,  again 
eliminated  and  carried  away  by  the  blood.  In  the  death- 
stiffening  this  elimination  cannot  occur,  the  circulation 
of  the  blood  having  ceased.     For  this  reason  death- 


88  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

stiffening  intervenes  much  more  quickly  in  muscles 
which  have  been  strongly  irritated  before  death,  as  for 
instance  in  those  of  hunted  animals.  But  while  the 
formation  of  acid  must  always  be  very  slight  in  active 
muscle,  it  increases  greatly  in  muscles  which  have  un- 
dergone death-stiffening,  and  the  acid  acts  as  a  relax- 
ing agent  on  the  connective  tissue  which  holds  the 
fibres  together,  so  that  the  latter  separate  more  readily. 
At  the  same  time,  however,  another  distinct  change 
occurs  within  the  muscle-fibre.  If  a  fresh  living  muscle- 
fibre  and  one  that  has  undergone  death-stiffening  are 
examined  under  the  microscope,  the  latter  appears  dull 
and  opaque ;  the  transverse  striations  are  narrower  and 
approach  more  nearly  together,  and  the  contents  are 
not  active  and  fluid,  as  in  the  living  fibre,  but  are  fixed 
and  broken  into  fragments.  When  unextended  muscles 
undergo  death-stiffening,  they  usually  become  shorter 
and  thicker.  In  the  mobile  facial  muscles  of  a  dead 
body  the  result  of  this  is  that  the  lines,  which  imme- 
diately after  death  were  relaxed,  again  acquire  a  certain 
expression.  The  death-stiffening  of  the  muscles  is  the 
cause  of  a  certain  rigidity  in  the  limbs  of  corpses,  so 
that  the  limbs  are  retained  in  the  same  relative  posi- 
tion in  which  they  were  at  death ;  and  it  is  to  this 
circumstance  that  the  name  *  death-stiffening  '  {rigor 
mortis)  is  principally  due.  Moreover,  this  change  does 
not  occur  simultaneously  in  the  muscles  of  all  parts  of 
the  dead  body ;  it  usually  begins  in  the  muscles  of  the 
face  and  neck  and  passes  gradually  downward,  so  that 
the  muscles  of  the  legs  are  the  last  to  be  affected  by 
it.  The  relaxation  of  the  rigidity  takes  place  in  the 
same  order. 

On  account  of  the  shortening  undergone  by  muscles 


DEATH-STIFFENING.  89 

during  death-stiifness  it  was  formerly  believed  that  the 
latter  was  to  be  regarded  as  a  true  contraction,  as  a  last 
exertion  of  muscular  force  in  which  the  muscle  took 
leave  of  its  peculiar  capacity.  There  is,  however,  nothing 
to  show  that  this  shortening  which  takes  place  at  death, 
and  which  may  moreover  be  hindered  by  the  application 
of  even  a  slight  weight,  corresponds  in  any  way  with 
the  real  state  of  activity.  All  the  phenomena  of  mus- 
cular rigidity  are,  indeed,  more  fully  explained  by  the 
assumption  that  some  constituent  part  of  the  muscle 
Avhich  is  liquid  in  the  living  muscle  becomes  fixed  or 
coagulates.  Death-stiffening  would  accordingly  be  a 
process  analogous  to  the  coagulation  of  the  blood,  which 
after  death  or  after  it  has  been  allowed  to  escape  from 
the  blood-vessels  becomes  firm,  in  consequence  of  the 
fact  that  one  of  its  constituents,  the  blood  fibrous  matter, 
or  fibrine,  secretes  itself  as  a  solid.  This  view  of  death- 
stiffness  was  first  expressed  by  E.  Briicke  and  was  after- 
ward confirmed  by  Kiihne.  If  the  muscles  of  a  frog  are 
freed  from  all  blood  by  injection  with  an  innocuous 
fluid,  such  as  a  weak  solution  of  common  salt,  and  are 
then  pressed,  a  fluid  is  obtained  which  represents  part 
of  the  liquid  contents  of  the  muscle-fibres.  If  this  fluid 
is  allowed  to  stand  for  some  hours  in  the  ordinary  tem- 
perature of  a  room,  a  flaky  clot  forms  in  it  at  the  same 
period  at  which  other  muscles  of  the  same  animal 
undergo  death-stiffening.  The  expressed  muscle-fluid 
is  originally  quite  neutral ;  but  while  the  clot  is  forming 
it  becomes  continually  more  acid.  The  resemblance  of 
the  process  in  this  muscle-fluid  to  that  in  the  muscle 
itself  is,  therefore,  such  as  to  justify  the  assumption 
that  at  the  same  time  a  coagulation,  simvdtaneously 
with  an  acid-formation,  takes  pla:ce  within  the  muscle 


DO  PHYSIOLOGY   OF   MUSCLES   AND   NERVES. 

itself,  and  that  this  coagulation  represents  the  essential 
fact  in  death-stiffening. 

Death-stiffening  intervenes,  as  we  found,  earlier 
in  proportion  as  the  temperature  is  higher.  Exactly 
the  same  is  the  case  in  expressed  muscle-fluid.  If  it 
is  heated  to  a  temperature  of  45°  C.  it  coagulates 
in  a  few  minutes,  becoming  acid  at  the  same  time. 
Muscles  also,  if  they  are  heated  to  a  temperature  of 
45°  C,  undergo  death-stiffening  in  a  few  minutes.  If 
they  are  still  further  heated,  up  to  or  above  a  tempe- 
rature of  73°  C,  they  contract  into  shapeless  lumps, 
become  quite  hard  and  white,  and  exhibit  a  Arm  solid 
tissue  resembling  the  white  of  eggs  when  cooked. 
From  this  it  may  be  inferred  that,  besides  the  matter 
which  coagulates  during  the  death- stiffening,  other 
soluble  albuminous  bodies  are  also  present  in  muscle, 
and  that  these  act  as  ordinary  albunaen  as  it  occurs  in 
blood  and  in  eggs  ;  for  the  latter  also  coagulates  when 
heated  to  73°  0.  It  therefore  appears  that  various  kinds 
of  albumen  occur  in  muscle.  That  which  coagulates 
at  45°,  or,  though  somewhat  more  slowly,  in  the  or- 
dinary temperature  of  a  room,  is  called  myosin.  It 
may  be  assumed  that  this  albiuninous  body  is  natu- 
rally soluble,  but  that  it  is  rendered  insoluble  by  the 
acids  occurring  within  the  muscle.  Dea.th-stiffening 
Avould  accordingly  be  the  result  of  the  formation  of 
acid.  Our  knowledge  on  this  point  is,  however,  yet 
very  incomplete,  and  must  remain  so  until  chemistry 
has  afforded  more  full  explanation  of  the  nature  of 
albuminous  bodies. 


CHAPTEB  VI. 

1.  Forms  of  muscle  ;  2,  Attachment  of  muscles  to  the  bones;  3. 
Elastic  tension ;  4.  Smooth  muscle-fibres ;  5.  Peristaltic  motion ; 
6.  Voluntary  and  involuntary  motion. 

1.  In  examining  the  action  of  muscle  in  the  previous 
chapters  we  have  invariably  dealt  with  an  imaginary 
muscle  the  fibres  of  which  were  of  equal  length  and 
parallel  to  each  other.  Such  muscles  do  really  exist, 
but  they  are  rare.  When  such  a  muscle  shortens,  each 
of  its  fibres  acts  exactly  as  do  all  the  others,  and  the 
whole  action  of  the  muscle  is  simply  the  sum  of  the 
separate  actions  of  all  the  fibres.  As  a  rule,  however, 
the  structure  of  muscles  is  not  so  simple.  According 
to  the  form  and  the  arrangement  of  the  fibres,  anatomists 
distinguish  short,  long,  and  fiat  muscles.  The  last- 
mentioned  generally  exhibit  deviations  from  the  ordinary 
parallel  arrangement  of  the  fibres.  Either  the  fibres 
proceed  at  one  end  from  a  broad  tendon,  and  are  directed 
towards  one  point  from  which  a  short  round  tendon 
then  effects  their  attachment  to  the  bones  (fan-shaped 
muscles) ;  or  the  fibres  are  attached  at  an  angle  to  a 
long  tendon,  from  which  they  all  branch  off  in  one 
direction  (semi-pennate  muscles),  or  in  two  directions 
like  the  plumes  of  a  feather  (pennate  muscles).  In  the 
radiate  or  fan-shaped  muscles  the  pull  of  the  separate 
parts  takes  efi"ect  in  different  directions.    Each  of  these 


92  PHYSIOLOGY   OF  MUSCLES  AND  NERVES. 

parts  may  act  separately,  or  all  may  work  together ;  and 
in  the  latter  case  they  combine  their  forces,  as  is  inva- 
riably the  case  with  forces  acting  in  different  directions, 
in  accordance  with  the  so-called  parallelogram  of  forces. 
As  an  example  of  this  sort  of  muscle  the  elevator  of  the 
upper  arm — which  was  before  alluded  to  in  the  second 
chapter,  and  which  on  account  of  its  triangular  shape  is 
called  the  deltoid  muscle — may  be  examined.  Contrac- 
tions of  the  separate  parts  really  occur  in  this.  When 
only  the  front  section  of  the  muscle  contracts,  the  arm  is 
raised  and  advanced  in  the  shoulder  socket ;  when  only 
the  posterior  part  of  the  muscle  contracts,  the  arm  is 
raised  backward.  WTien,  however,  all  the  fibres  of  the 
muscle  act  in  unison,  the  action  of  all  the  separable  forces 
of  tension  constitute  a  diagonal  which  results  in  the 
lifting  of  the  arm  in  the  plane  of  its  usual  position. 

In  some  semi-pennate  and  pennate  muscles  the  line  of 
union  of  the  t^^o  points  of  attachment  does  not  coincide 
with  the  direction  of  the  fibres.  When  the  muscle  con- 
tracts each  fibre  exerts  a  force  of  tension  in  the  direction 
of  its  contraction.  All  these  numerous  forces,  however, 
produce  a  single  force  which  acts  in  the  direction  in 
which  the  movement  is  really  accomplished,  and  the 
whole  action  of  the  muscle  is  the  sum  of  these  separate 
components,  each  derived  from  a  single  fibre.  In 
order  to  calculate  the  force  which  one  of  these  muscles 
can  exert,  as  well  as  the  height  of  elevation  proper  to 
it,  it  would  be  necessary  to  determine  the  number  of 
the  fibres,  the  angle  which  each  of  these  makes,  with 
the  direction  finally  taken  by  the  compound  action,  as 
well  as  the  length  of  the  fibres — these  not  being  always 
equal.  This  task  if  only  carried  out  in  the  case  of  a  single 
muscle  would  be  a  very  great  test  of  patience      Fortu- 


ATTACmiENT   OF  MUSCLES  TO    BOXES.  93 

natelj  no  such  tedious  calculations  are  requisite  for  our 
purpose.  The  force  may  be  directly  determined  by  ex- 
periment in  the  case  of  many  muscles,  by  the  method 
already  described  in  Chapter  IV.  §  6 ;  the  height  of 
elevation  possible  under  the  conditions  present  in  the 
body  may  be  yet  more  easily  found ;  and  as  regards  the 
work  which  the  muscle  is  able  to  perform,  it  makes  no 
difference  whether  the  fibres  are  all  parallel  and  act  in 
their  own  direction,  or  if  they  form  any  angle  with  the 
direction  of  work.^ 

2.  The  direction  in  which  the  action  takes  effect 
does  not,  however,  depend  only  on  the  structure  of  the 
muscle,  but  chiefly  on  the  nature  of  its  attachment  to 
the  bone.  Owing  to  the  form  of  the  bones  and  their 
sockets,  the  points  of  connection  by  which  the  bones 
are  held  together,  the  bones  are  capable  of  moving  only 
within  certain  limits,  and  usually  only  in  certain  direc- 
tions. For  instance,  let  us  watch  a  true  hinge-socket, 
such  as  that  of  the  elbow,  which  admits  only  of  bending 
and  stretching  {cf.  ch.  ii.  §  4).  As  in  this  case,  the 
nature  of  the  socket  is  such  that  motion  is  only  possible 
in  one  plane,  the  muscles  which  do  not  lie  in  this  plane 
can  only  bring  into  action  a  portion  of  their  power  of 
tension,  and  this  may  be  found  if  the  tension  exercised 
by  the  muscle  is  analysed  in  accordance  with  the  law 
of  the  parallelogram  of  forces,  so  as  to  find  such  of  the 
component  forces  as  lie  within  the  plane. 

It  is  different  in  the  case  of  the  more  free  ball- 
sockets,  which  permit  movement  of  the  bone  in  any 
direction  within  certain  limits.  When  a  socket  of  this 
sort  is  surrounded  by  many  muscles,  each  of  the  latter, 
if  it  acts  alone,  sets  the  bone  in  motion  in  the  direction 
'  See  Notes  and  Additions,  No  2. 


94  PHYSIOLOGY    OF    MUSCLES   AND   NERVES. 

of  its  own  action.  If  two  or  more  of  the  muscles  as- 
sume a  state  of  activity  at  tlie  same  time,  then  the  action 
will  be  the  resultant  of  the  separate  tensions  of  each, 
and  this  may  also  be  found  by  the  law  of  the  parallelo- 
gram of  forces. 

There  is  yet  another  way  in  which  the  work  per- 
formed by  the  muscles  is  conditioned  by  their  attach- 
ment to  the  bones.  The  latter  must  be  regarded  as 
levers  which  turn  on  axes,  afforded  by  the  sockets. 
They  usually  represent  one-armed,  but  sometimes  two- 
armed  levers.  Now,  the  direction  of  the  tension  of 
the  muscles  is  seldom  at  right  angles  to  that  of  the 
moveable  bone  lever,  but  is  usually  at  an  acute  angle. 
In  this  case,  again,  the  whole  tension  of  the  muscle 
does  not  take  effect,  but  only  a  component,  which  is  at 
right  angles  to  the  arm  of  the  lever.  Now,  it  is  notice- 
able that  in  many  cases  the  bones  have  projections 
or  protrusions  at  the  point  of  the  attachment  of  the 
muscles,  over  which  the  muscle  tendon  passes,  as  over 
a  reel,  thus  grasping  the  bone  at  a  favourable  angle ; 
or,  in  other  cases,  it  is  found  that  cartilaginous  or  bony 
thickenings  exist  in  the  tendon  itself  (so-called  sesam- 
oid bones),  which  act  in  the  same  way.  The  largest  of 
these  sesamoid  bones  is  that  in  the  knee,  which,  in- 
serted in  the  powerful  tendon  of  the  front  muscle  of 
the  upper  thigh,  gives  a  more  favourable  direction  to 
the  attachment  of  this  tendon  than  there  would  other- 
wise be. 

Sometimes  the  tendon  of  a  muscle  passes  over  an 
actual  reel,  so  that  the  direction  in  which  the  muscle- 
fibres  contract  is  entirely  different  from  that  in  which 
their  force  of  tension  acts. 

3.  The  last  important  consequence  of  the  attach- 


ELASTIC   TENSION.  95 

ment  of  the  muscles  to  the  bones  is  the  extension  thus 
effected.  If  the  limb  of  a  dead  body  is  placed  in  the 
position  %Yhich  it  ordinarily  occupied  during  life,  and  if 
one  end  of  a  muscle  is  then  separated  from  its  point 
of  attachment,  it  draws  itself  back  and  becomes  shorter. 
The  same  thing  happens  during  life,  as  is  observable  in 
the  operation  of  cutting  the  tendons,  as  practised  by 
surgeons  to  cure  curvatures.  The  result  being  the  same 
dming  life  and  after  death,  this  phenomenon  is  evi- 
dently due  to  the  action  of  elasticity.  It  thus  appears 
that  the  muscles  are  stretched  by  reason  of  their  attach- 
ment to  the  skeleton,  and  that,  on  account  of  their  elas- 
ticity, they  are  continually  striving  to  shorten.  Now, 
when  several  muscles  are  attached  to  one  bone  in  such 
a  way  that  they  pull  in  opposite  directions,  the  bone 
must  assume  a  position  in  which  the  tension  of  all  the 
muscles  is  balanced,  and  all  these  tensions  must  com- 
bine to  press  together  the  socketed  parts  with  a  certain 
force,  thus  evidently  contributing  to  the  strength  of  the 
socket  connection.  When  one  of  these  muscles  con- 
tracts, it  moves  the  bone  in  the  direction  of  its  own 
tension,  but  in  so  doing  it  extends  the  muscle  which 
acts  in  an  opposite  direction,  and  the  latter,  because  of 
its  elasticity,  offers  resistance  to  the  tension  exerted  by 
the  first  muscle,  so  that  as  soon  as  the  contraction  of 
the  latter  is  relaxed  the  limb  falls  back  again  into  its 
original  position.  This  balanced  position  of  all  the 
limbs,  which  thus  depends  on  the  elasticity  of  the 
muscles,  may  be  observed  during  sleep,  for  then  all  ac- 
tive muscular  action  ceases.  It  will  be  observed  that 
the  limbs  are  then  generally  slightly  bent,  so  that  they 
form  very  obtuse  angles  to  each  other. 

Not  all   muscles  are,  however,  extended  between 


96  PHYSIOLOGY   OF   MUSCLES  AND   NERVES. 

bones.  The  tendons  of  some  pass  into  soft  structures, 
such  as  the  muscles  of  the  face.  In  this  case  also  the 
different  muscles  exercise  a  mutual  power  of  extension, 
though  it  is  but  slight,  and  they  thus  effect  a  definite 
balanced  position  of  the  soft  parts,  as  may  be  observed 
in  the  position  of  the  mouth-opening  in  the  face.  If 
the  tension  of  the  muscles  ranged  on  both  sides  is  not 
equal,  the  mouth  opening  assumes  a  crooked  position. 
This  happens,  for  example,  when  the  muscles  of  one 
half  of  the  face  are  injinred ;  and  it  thus  appears  that  in 
this  case  the  elastic  tension  is  too  weak  to  allow  of  the 
retention  of  the  normal  position  of  the  mouth. 

In  muscles  attached  to  bones  the  elastic  tension  is, 
however,  much  greater,  a  circiunstance  which  naturally 
exercises  an  influence  on  their  action  during  contrac- 
tion. 

4.  As  yet  attention  has  only  been  paid  to  one  kind 
of,  muscle-fibre,  that  which  from  the  very  first  we  dis- 
tinguished as  striated  fibre.  There  is,  however,  as  we 
have  seen,  another  kind,  the  so-called  smooth  muscle- 
fibre.  These  are  long  spindle-shaped  cells,  the  ends  of 
which  are  frequently  spirally  twisted,  and  in  the  centre 
of  which  exists  a  long  rod-shaped  kernel  or  nucleus. 
Unlike  striated  muscle,  they  do  not  form  separate  mus- 
cular masses,  but  occur  scattered,  or  arranged  in  more 
or  less  dense  layers  or  strata,  in  almost  all  organs.^ 
Arranged  in  regular  order,  they  very  frequently  form 
widely  extending  membranes,  especially  in  such  tube- 
shaped  structures  as  the  blood-vessels,  the  intestine, 

1  An  instance  of  a  considerable  accumulation  of  sfmooth  muscle- 
fibres  is  afforded  by  tlie  muscle-pouch  of  birds,  which,  with  the  ex- 
ception of  the  outer  and  inner  skin  coverings,  consists  solely  of  these 
fibres  collected  in  extensive  layers. 


SMOOTH   MUSCLE-FIBRES. 


97 


&c.,  the  walls  of  which  are  composed  of  these  smooth 
muscle-fibres.  In  such  cases  they  are  usually  arranged 
in  two  ]ayers,  one  of  which  consists  of  ring-shaped  fibres 
surrounding  the  tube,  while  the  other  consists  of  fibres 
arranged  parallel  to  the  tube.  When,  therefore,  these 
muscle-fibres   contract,  they   are  able  both  to  reduce 


Fig.  25.     Smouth  .MLSCLii-Kiisiiiis  (oOO  toiks  enlarged). 

the  circumference,  and  to  shorten  the  length  of  the 
walls  of  the  tube  in  which  they  occur.  This  is  of  great 
importance  in  the  case  of  the  smaller  arteries,  in  which 
the  smooth  muscle-fibres,  arranged  in  the  form  of  a 
ring,  are  able  greatly  to  contract,  or  even  entirely  to 
close  the  vessels,  thus  regulating  the  current  of  blood 
through  the  capillaries.  In  other  cases,  as  in  the  in- 
testine, they  serve  to  set  the  contents  of  the  tubes  in 
motion.     In  the  latter  cases  the  contraction  does  net 


98  PHYSIOLOGY   OF    MUSCLES   AND   NERVES. 

take  place  simultaneously  througliout  the  length  of  the 
tube ;  but,  commencing  at  one  point,  it  continually 
propagates  itself  along  fresh  lengths  of  the  tube,  so  that 
the  contents  are  slowly  driven  forward.  The  principal 
agents  in  this  are  the  circularly  arranged  fibres,  which 
at  one  point  completely  close  the  tube,  while,  by  the 
contraction  of  the  longitudinal  fibres,  the  wall  of  the 
tube  is  drawn  back  over  its  contents,  thus  providing  for 
the  propulsion  of  the  contents.  This  is  called  peri- 
staltic motion.  It  takes  place  along  the  whole  of  the 
digestive  canal,  from  the  throat  to  the  other  end,  and 
in  this  case  affects  the  forward  motion  of  the  food,  as 
also,  finally,  the  expulsion  of  the  undigested  residue. 

5.  Peristaltic  motion  may  be  very  well  observed  by 
laying  bare  the  throat  of  a  dog,  and  then  placing  water 
in  the  mouth  of  the  animal,  so  that  the  motion  of  swal- 
lowing takes  place.  It  may  also  be  seen  in  the  intes- 
tines when  laid  bare,  as  also  in  the  urinary  duct,  in 
which  each  drop  of  urine  leaving  the  kidneys  produces 
a  wave  which  propagates  itself  from  the  kidneys  to  thj 
urinary  bladder.  Such  movements  may  also  be  artifi- 
cially elicited  by  mechanically  or  electrically  irritating 
some  one  point  of  the  intestine,  urinary  duct,  or  other 
such  part,  or  by  irritating  the  nerves  appropriate  to 
these  parts.  The  most  striking  feature  is  the  slowness 
with  which  these  motions  take  place.  Not  only  does  a 
long  time,  observable  without  any  artificial  aid,  elapse 
after  the  application  of  the  irritant  before  the  motion 
begins,  but,  even  if  the  irritation  is  sudden  and  in- 
stantaneous, the  motion  excited  at  one  point  passes 
along  very  gradually,  slowly  increasing  up  to  a  definite 
point,  and  then  again  gradually  decreasing.  This  slow- 
ness of  motion  essentially  distinguishes  smooth  from 


PERISTALTIC   MOTION.  99 

striated  muscle-fibres.  But,  as  we  know,  this  is  not  a 
distinction  of  kind,  but  only  one  of  degree;  for  we 
found  that  in  the  case  of  striated  muscle  also  there  is 
a  stage  of  latent  irritation,  then  a  gradually  increas- 
ing, and  then  again  a  gradually  decreasing  contraction. 
But  that  which  in  striated  muscle  occupies  but  a  few 
parts  of  a  second,  in  smooth  muscle-fibres  occupies  a 
period  of  several  seconds.  No  artificial  aid  is,  there- 
fore, required  in  this  case  to  distinguish  the  separate 
stages.  At  present,  research  into  the  nature  of  smooth 
muscle-fibre  has  not  resulted  in  the  acquirement  of  more 
than  this  somewhat  superficial  knowledge.  Owing  espe- 
cially to  the  difficulty  of  isolating  the  fibres,  and  to  the 
rapidity  with  which  they  lose  their  irritability  when 
separated  from  the  body,  it  is  very  difficult  to  experi- 
ment with  them.  It  is  especially  not  yet  clear  by  what 
means  the  transference  of  the  irritation  arising  at  one 
point  to  the  other  part  is  effected.  The  transference 
never  occurs  in  the  case  of  striated  muscle.  If  a  long, 
thin,  parallel-fibred  muscle  is  separated  out  on  a  glass 
plate,  and  a  very  small  part  of  it  is  then  irritated,  the 
irritation  immediately  propagates  itself  in  a  longitudirsal 
direction  in  the  muscle-fibre  immediately  touched.  It 
is  impossible  to  produce  contraction  in  a  striated  muscle- 
fibre  only  at  one  point  in  its  length,  at  least  while  the 
muscle-fibre  is  fresh.  In  dpng  muscle-fibres  such  local 
contractions  do  indeed  occur.  Each  separate  muscle- 
fibre,  therefore,  forms  a  closed  whole  in  which  the  con- 
traction excited  at  one  point  spreads  over  the  whole 
fibre.  The  speed  with  which  it  spreads  within  the 
fibre  has  even  been  measured.  As  the  striated  muscle- 
fibre  in  contracting  becomes  also  thicker,  a  small  light 
lever,   if  attached   to  the  fibre,  is  somewhat  raised, 


100     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

and  this  rise  can  be  indicated  on  a  rapidly-moving 
myograph  plate.  If  two  of  these  small  levers  are 
placed  near  the  ends  of  a  long  muscle,  and  one  of  the 
ends  is  then  irritated,  the  nearer  lever  is  first  raised, 
the  more  remote  not  till  later.  This  difference  may  be 
read  off  the  plate  of  the  myograph,  and  thus  the 
speed  of  the  propagation  from  one  lever  to  the  other 
may  be  calculated.  Aeby,  who  first  tried  this  experi- 
ment, found  that  the  speed  was  from  one  to  two  metres 
in  the  second,  or,  in  other  words,  that  a  contraction 
excited  at  one  point  of  a  muscle-fibre  requires  a  period 
of  from  about  -^-i^  to  y^  of  a  second  to  advance  one 
centimetre.  More  recent  measurements  by  Bernstein 
and  Hermann  show  the  higher  value  of  from  three  to  four 
metres  in  the  second.  On  the  death  of  the  muscle, 
the  rate  of  propagation  becomes  continually  less,  finally 
ceasing  entirely  in  muscles  which  are  just  about  to  pass 
into  a  state  of  death-stiffness,  so  that  on  irritation  only 
a  slight  thickening  is  seen  at  the  point  directly  irritated, 
and  this  does  not  propagate  itself.  Under  all  circum- 
stances, however,  the  excited  contraction  is  confined  to 
the  fibres  which  are  themselves  actually  irritated,  the 
neighbouring  fibres  remaining  perfectly  quiescent.  In 
smooth  muscle-fibres,  however,  it  is  found  that  the 
contractions  excited  at  one  point  propagate  themselves 
in  the  adjacent  fibres  also.  The  marked  distinction 
which  thus  appears  to  exist  between  smooth  and  striated 
muscles  would,  it  is  true,  disappear  if  the  views  of 
Engelmann,  resulting  from  his  study  of  the  urinary 
duct,  are  confirmed.  According  to  that  writer,  the 
muscular  mass  of  the  urinary  duct  does  not  consist 
during  life  of  separate  muscle-fibre  cells,  but  forms 
a  homogeneous    connected  mass  which  only  separates 


VOLUNTARY    AND    INVOLUNTARY    MOTION.  101 

into  spindle-shaped  cells  at  death.  If  this  view  could 
also  be  extended  to  the  smooth  muscle  masses  of  other 
parts,  a  real  connection  would  exist  throughout  the 
muscle-membranes,  and  the  phenomena  of  the  propaga- 
tion of  irritation  would  admit  of  a  physiological  explana- 
tion. 

6.  As  a  rule,  such  parts  as  are  provided  only  with 
smooth  muscle-fibres  are  not  voluntarily  movable,  while 
striated  muscle-fibres  are  subject  to  the  will.  The  latter 
have,  therefore,  been  also  distinguished  as  voluntary, 
the  former  as  involuntary  muscles.  The  heart,  however, 
exhibits  an  exception,  for,  though  it  is  provided  with 
striated  muscle-fibres,  the  will  has  no  direct  influence 
upon  it,  its  motions  being  exerted  and  regulated  inde- 
pendently of  the  will.'  Moreover,  the  muscle-fibres  of 
the  heart  are  peculiar  in  that  they  are  destitute  of  sar- 
colemma,  the  naked  muscle-fibres  directly  touching  each 
other.  This  is  so  far  interesting  that  direct  irritations, 
if  applied  to  some  point  of  the  heart,  are  transferred 
to  all  the  other  muscle-fibres.  In  addition  to  this, 
the  muscle-fibres  of  the  heart  are  branched,  but  such 
branched  fibres  occur  also  in  other  places,  for  example, 
in  the  tongue  of  the  frog,  where  they  are  branched  like 
a  tree.  Smooth  muscle-fibres  being,  therefore,  not  sub- 
ject to  the  will,  are  caused  to  contract,  either  by  local 
irritation,  such  as  the  pressure  of  the  matter  contained 
within  the  tubes,  or  by  the  nervous  system.  The  con- 
tractions of  striated  muscle-fibres  are  effected,  in  the 
natural  course  of  organic  life,  only  by  the  influence  of 

'  Striated  muscles  also  occur  iu  the  intestine  of  the  tench 
{Tinea  vuhjaris),  which  in  this  differs  from  all  other  vertebrate  ani- 
mals. It  is  doubtful  whether  tliis  tissue  is  capable  of  voluntary 
motion,  but  it  is  very  improbable. 


102     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

the  nerves.  We  must  now,  therefore,  examine  the 
characters  of  nerves,  after  which  we  shall  try  to  explain 
the  nature  of  their  influence  on  muscles. 

It  must  also  be  observed  that  the  distinction  between 
striated  and  smooth  muscle-fibres  is  not  absolute ;  for 
there  are  transitionary  forms,  such  as  the  muscles  of 
molluscs.  The  latter  consist  of  fibres,  exhibiting  to 
some  extent  a  striated  character,  and,  in  addition  to 
this,  the  character  of  double  refraction.  At  these  points 
the  disdiaclasts  are  probably  arranged  regularly  and  in 
large  groups,  while  at  other  points  (as  in  true  smooth 
muscle-fibres)  they  are  irregularly  scattered  and  are 
therefore  not  noticeable. 


CHAPTER  VII. 

1.  Nerve-fibres  and  nerve-cells ;  2.  Irritability  of  nerve-fibre ; 
3.  Transmission  of  the  irritation ;  4.  Isolated  transmission ; 
5.  Irritability;  6.  The  curve  of  irritability;  7.  Exhaustion  and 
recoverj',  death. 

1.  In  the  body  of  an  animal  nerves  occur  in  two  forms : 
either  as  separate  delicate  cords  which  divide  into  many 
parts  and  distribute  themselves  throughout  the  body, 
or  collected  in  more  considerable  masses.  The  latter, 
at  least  in  the  higher  animals,  are  enclosed  in  the  bony 
eases  of  the  skull  and  vertebral  column,  and  are  called 
nerve-centres,  or  central  organs  of  the  nervous  system ; 
the  nerve-cords  pass  from  these  centres  to  the  most 
distant  parts,  and  are  spoken  of  as  the  ^peripheric  nerve- 
system.  When  examined  under  the  microscope  these 
peripheric  nerves  are  seen  to  be  bundles  of  extremely 
delicate  fibres  united  into  thicker  bands  within  a  mem- 
brane of  connective  tissue.  Each  of  these  nerve-fibres 
when  examined  in  a  fresh  state,  and  enlarged  250  or 
300  times,  is  exhibited  as  a  pale  yellow  transparent 
fibre  in  which  no  further  difierentiation  is  visible.  The 
appearance  of  the  fibre  soon,  however,  changes ;  it  be- 
comes less  transparent,  and  a  part  lying  along  the  axis 
becomes  marked  off  from  the  circumference.  This  inner 
part  is  usually  flat  and  band-like,  and  when  seen  under 
a   higher    power  exhibits  a  very  minute  longitudinal 


104 


PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 


striation,  as  though  it  were  formed  of  very  delicate 
fibrillse,  or  small  fibres.  It  is  called  the  axis-band,  or 
axis -cylinder.  The  outer  part  has  a  crumpled  appear- 
ance, and  oozes  at  the  cut  ends  of  the  nerve  in  drops 
which  soon  coagulate ;  it  is  called  the  niedidlary,  or 
marroiv-shexth.  The  medullary  sheath  entirely  sur- 
rounds the  axis-cylinder ;  as,  however,  when  in  a  fresh, 

uncoagulated  condition,  it  re- 
fracts light  in  exactly  the  same 
way  as  the  axis-cylinder,  it 
is  undistinguishable  from  the 
latter,  nor  do  the  two  become 
really  separately  visible  till 
after  the  coagulation  of  the 
marrow.  The  medullary- 
sheath  and  the  axis-cylinder 
are  further  enclosed  in  a 
tough  elastic  tube,  which  is 
called  the  neurilemr,ia  or 
nerve-sheath. 

These  three  parts  are  not 
present  in  all  peripheric 
nerves.     Some   of  the  latter 

surrounded  by  the  medullary  sheath;    j^^^.^     ^^     mcdulkry      shcath, 

and  are,  therefore,  axis-cylinders  immediately  sur- 
rounded by  the  nerve-sheaths.  When  many  nerve- 
fibres  are  united  into  a  bundle,  these  marrowless  fibres 
are  grey  and  more  transparent,  and  are  therefore  some- 
times called  grey  nerve-fibres.  Those  nerve-fibres  which 
have  medullary  sheaths  appear  more  yellowish  white.  If 
the  nerves  are  traced  to  the  periphery,  more  and  more 
nerve-fibres  are  continually  found  to  branch  off  from 
the  common  stem,  so  that  the  branches  and  branchlets 


Fig.  23.     Xerve-Fibres. 
a  a,   the   axis-cylinder,  still  partially 


XERVE-FIBRES    AND    NERVE-CELLS.  105 

gradually  become  thinner.  At  last  only  separate  fibres 
are  to  be  seen,  these  being,  however,  still  in  appearance 
exactly  like  those  constituting  the  main  stem.  Such 
fibres  as  up  to  this  point  have  had  medullary  sheaths  ' 
now  frequently  lose  them,  and  therefore  become  exactly 
like  grey  fibres.  The  axis-cylinder  itself  then  some- 
times separates  into  smaller  parts  ;  so  that  a  nerve-fibre, 
thin  as  it  is,  embraces  a  very  large  surface.  The  ends  of 
the  nerve-fibres  are  connected  sometimes  with  muscles, 
sometimes  with  glands,  and  sometimes,  again,  with 
peculiar  terminal  organs. 

In  the  central  organs  of  the  nervous  system  many 
nerve-fibres  are  found  which  are  in  appearance  in- 
distinguishable from  those  of  the  peripheric  system. 
There  are  fibres  with  axis-cyhnder,  medullary  sheath, 
and  neurilemma,  others  without  medullary  sheuth,  and, 
finally,  others  in  which  no  neurilemma  can  be  detected, 
and  which  may  therefore  be  described  as  naked  axis- 
cylinders.  But,  besides  these,  very  delicate  fibres,  far 
finer  than  the  axis-cylinders,  occur.  The  central  organs 
of  the  nervous  system  are  however  especially  marked 
by  the  abundant  occurrence  of  a  second  element,  which, 
though  it  is  not  altogether  unrepresented  in  peripheric 
nerves,  yet  is  only  found  in  the  latter  distributed  in  a 
few  places,  whilst  in  the  central  organs  it  constitutes 
an  important  portion  of  the  whole  mass.  This  consists 
of  certain  cell-like  structures  called  nerve-cells,  or  gan- 
glian-cells.  In  each  ganglion-cell  it  is  possible  to  dis- 
tinguish the  cell  body,  and  a  large  kernel  (^lucleus') 
within  this;  within  the  kernel,  a  smaller  kernel  (nu- 
cleolus^ may  also  frequently  be  distinguished.  Some 
ganglion-cells  are  also  surrounded  by  a  membrane 
which  occasionally  passes  into  the  neurilemma  of 
6 


106 


PHYSIOLOGY   OF   MUSCLES   AlSfD   NERVES. 


nerve-fibres,  wliicli  are  connected  with  the  cell.  The 
kernel  is  finely  granulated  and  is  composed  of  a  pro- 
toplasmic mass,  which,  when 
heated,  or  subjected  to  certain 
other  influences,  becomes  dull 
and  opaque,  but  which  in  a  fresh 
condition  is  usually  somewhat 
transparent.  The  form  of  the 
ganglion-cells  is  very  variable. 
Sometimes  they  appear  almost 
globular;  in  other  cases  they 
are  elliptic  ;  others,  again,  are 
irregular,  provided  with  numer- 
ous offshoots.  Most  ganglion- 
cells  have  one  or  more  project- 
ing processes ;  some  are,  indeed, 
found  without  processes,  but  it 
is  certain  that  this  condition  is 
merely  artificially  produced,  the 
processes  having  been  torn  off 
during  the  preparation  of  the 
ganglion  -  cell.  Ganglion  -  cells 
are  occasionally  inserted  in  the 
course  of  the  nerve-fibres,  so 
that  the  processes  differ  in  no 
way  from  other  nerve-fibres,  as 
is  shown  in  fig.  27.  In  the  gan- 
glion-cells of  the  dorsal  marrow, 

which     have    many     processes. 
Fig.  2/.    Gaxglion-celi.s  ^       j- 

wiTH  NERVE-PROCESSES,      somc    of  thcsc    appear    exactly 

like  the  rest  of  the  cell  body — 

that  is  to  say,  they  are  finely  granulated ;    these  are 

called  protoplasmic  processes.     On  the  other  hand,  in 


NERVE-FIBRES    AND    NERVE-CELLS.  107 

almost  every  cell  a  process  may  be  distinguished  which 
is  altogether  distinct  in  appearance  from  the  rest.  The 
protoplasmic  processes  become  gradually  finer  and  sepa- 
rate into  more  parts,  and  the  processes  of  neighbom-ing 
cells  are  partly  connected  together.  But  the  one  pro- 
cess which  is  distinguishable  from  the  rest  passes  along 
for  a  certain  distance  as  a  cylindrical  cord,  and  then, 
suddenly  becoming  thicker,  it  encases  itself  in  a  me- 
dullary sheath,  and  in  appearance  entirely  resembles 
the  medullary  fibres  of  the  peripheric  system.  It  is 
extremely  probable,  although  it  is  hard  to  prove  it  with 
certainty,  that  a  fibre  of  this  sort  passing  out  of  the 
dorsal  marrow  is  directly  transformed  into  a  peripheric 
nerve-fibre,  while  the  protoplasmic  processes  continu- 
incr  on  their  course  within  the  central  orp'an  serve  to 
connect  the  ganglion-cells. 

The  nerve-system,  the  main  parts  of  which  we  have 
thus  roughly  examined,  effects  the  motions  and  sensa- 
tions of  the  body.  These  qualities  belong,  however, 
mainly  to  the  central  parts,  in  which  ganglion-cells 
occur.  The  peripheric  nerve-fibres  act  merely  as  con- 
ducting or  transmitting  apparatus  to  or  from  the 
central  organs.  Before  examining  the  peculiar  action 
of  the  central  nervous  system,  it  is  desirable  to  devote 
some  attention  to  this  conducting  apparatus  and  to  dis- 
cover its  nature. 

2.  On  exposing  one  of  the  peripheric  nerves  of  a 
living  animal  and  allowing  irritants  to  act  upon  this, 
in  the  way  which  was  described  in  the  case  of  muscles, 
two  effects  are  usually  observable.  The  animal  suffers 
pain,  which  it  expresses  by  violent  motion  or  cries,  and, 
at  the  same  time,  individual  muscles  contract.  On 
tracing  the  irritated  nerve  to  the  periphery,  it  will  be 


108  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

found  that  certain  of  its  fibres  unite  with  those  muscles 
■which  pulsated.  We  already  know  that  the  other  end 
of  the  nerve  is  connected  with  the  nerve-centre.  If 
the  nerve  is  cut  at  a  point  between  the  irritated 
spot  and  the  nerve-centre,  the  muscular  pulsation 
occurs  as  before  on  the  re-application  of  the  irritant, 
but  the  sensation  of  pain  is  absent.  If,  on  the  other 
hand,  the  nerve  is  cut  at  a  point  nearer  the  periphery, 
no  muscular  pulsation  results  from  irritation,  but  pain 
is  felt.  It  thus  appears  that  the  peripheric  nerves, 
when  irritated  at  any  point  in  their  course,  are  able  to 
cause  effects  both  at  their  central  and  peripheric  ends, 
provided  that  the  conductive  power  of  the  nerves  re- 
mains uninjured  in  both  directions.  This  enables  us 
to  study  more  closely  the  action  of  the  nerves  on  the 
muscles,  by  extracting  and  preparing  a  portion  of  the 
nerve  with  its  muscle,  in  an  uninjured  condition,  and 
then  subjecting  this  nerve  to  further  research. 

That  a  nerve  is  irritable,  in  the  same  sense  as  we 
found  that  the  muscle  was,  is  already  shown  by  these 
preliminary  experiments.  But  while  it  was  possible 
to  observe  the  effects  of  the  irritation  on  the  muscle 
directly,  the  nerve  does  not  exhibit  any  immediate 
change,  either  in  form  or  appearance.  Even  under  the 
strongest  microscopic  power  nothing  is  discernible,  and 
it  would  be  impossible  to  know  if  a  nerve  is  in  any  way 
irritable  if  the  muscle  which  occurs  at  one  end  of  it 
did  not  show  by  its  pulsation  that  some  change  must 
have  occiurred  within  the  nerve.  The  muscle  is  there- 
fore used  as  a  re-agent  to  test  the  changes  in  the  nerve 
itself.  The  requisite  experiments  may  be  either  with 
warm-blooded  or  with  cold-blooded  animals.  As,  how- 
ever, the  muscles  of  warm-blooded  animals,  when  with- 


IRKITABILITY    OF  NERVE-FIBRES.  109 

drawri  from  the  influence  of  the  circulation  of  the  blood, 
soon  lose  their  power  of  activity,  the  nerves  and  muscles 
of  frogs  are  preferable  for  these  experiments.  The 
lower  part  of  the  thigh  of  a  frog,  with  a  long  portion  of 
the  sciatic  nerve,  which  is  very  easily  separable  up  to 
the  point  where  it  emerges  from  the  vertebral  column, 
is  best  suited  for  this  purpose.  In  some  cases  it  is 
better  to  use  only  the  calf-muscle  with  the  sciatic 
nerve ;  the  muscle  must  be  fastened  in  the  same  way 
as  in  the  former  experiments,  and  its  contractions  must 
be  made  evident  by  use  of  a  lever. 

If  the  muscle,  thus  fastened,  is  pinched  at  any  point 
in  its  course  it  pulsates.  The  same  result  follows  if  a 
thread  is  passed  round  the  nerve,  and  the  latter  is  thiis 
constricted,  or  if  a  small  piece  is  cut  from  the  nerve 
with  a  pair  of  scissors.  These  are  mechanical  irrit- 
ants which  act  on  the  nerve.  Pulsation  will,  however, 
also  be  seen  if  the  nerve  is  smeared  with  alkaline 
matter,  or  acid — these  are  chemical  irritants.  A  por- 
tion of  the  nerve  may  be  heated ;  that  is,  it  may  be 
thermically  irritated.  In  all  these  cases,  the  nerve  at 
the  point  irritated,  immediately,  or,  at  least  very  soon, 
loses  its  capacity  for  receiving  irritation.  But  if  the 
nerve  is  placed  on  two  wires,  by  means  of  which  an 
electric  current  is  passed  through  one  point  in  the 
nerve,  it  may,  in  this  way,  be  repeatedly  electrically 
irritated  withoilt  its  irritability  being  immediately  de- 
stroyed. It  therefore  appears  that,  in  this  respect,  a 
nerve  acts  exactly  as  does  a  muscle.  If  a  constant 
electric  current  is  applied,  the  result  is  usually  a  pul- 
sation on  the  closing  and  the  opening  of  the  current, 
but  sometimes  a  lasting  contraction  ensues  while  the 
current  flows  through  the   portion  of  the  nerve.     If 


110  PHYSIOLOGY    OF    MUSCLES   AND   NERVES. 

inductive  shocks  are  applied,  each  separate  shock  pro- 
duces a  muscular  pulsation,  and  if  many  separate  in- 
ductive shocks  are  applied  to  the  nerve,  the  muscle 
passes  into  a  state  of  tetanus.  These  inductive  shocks 
must  be  applied  to  the  nerve  at  some  distance  from 
the  muscle.  Each  inductive  shock  induces  a  muscu- 
lar pulsation.  On  cutting  the  nerve  with  a  pair  of 
scissors,  between  the  point  irritated  and  the  muscle, 
all  influence  upon  the  miuscle  ceases.  It  is  useless  to 
place  two  cut  surfaces  together,  even  with  the  greatest 
care;  they  may  adhere,  and  the  nerve,  when  super- 
ficially examined,  may  appear  uninjured,  but  irritants 
applied  above  the  point  of  section  cannot  act  through 
the  nerve  upon  the  muscle.  The  same  thing  occurs  if 
a  thread,  passed  round  the  nerve,  is  drawn  tight  be- 
tween the  point  irritated  and  the  muscle.  The  thread 
may  be  removed,  but  the  crushed  spot  proves  an  im- 
passable barrier  to  all  influence  on  the  muscle.  If, 
however,  the  wires  are  moved  and  the  inductive  cur- 
rents are  applied  to  another  point  below  the  cut  or  the 
constriction,  the  action  at  once  recommences. 

3.  The  conclusion  to  be  drawn  from  these  experi- 
ments is,  either  that  the  nerve,  even  if  only  a  small 
portion  of  it  is  irritated,  passes  at  once  into  an  active 
condition  throughout  its  entire  length  as  far  as  the 
muscle,  or  that  the  irritant  acts  directly  only  on  the 
spot  immediately  irritated,  and  that  the  activity  which 
is  excited  in  the  nerve  at  this  point  propagates  itself 
along  the  fibres  until  it  reaches  the  muscle  in  which  it 
causes  a  contraction.  If  the  latter  view  is  correct,  it 
must  also  be  inferred  that  any  injm'y  to  the  nerve-fibre 
prevents  the  propagation  of  the  activity  in  the  latter ; 
and  it  may  also  be  deduced  from  the  experiments  with 


TRANSMISSION    OF   THE   EXClTEMf:NT.  Ill 

the  constricted  nerves,  that  even  if  the  nerve-sheath  is 
in  no  way  injured,  the  crushing  of  the  contents  of  the 
nerve  is  in  itself  sufficient  to  prevent  propagation  of 
the  activity.  It  can  be  showa  that  this  latter  view 
of  the  natiu-e  of  the  case  is  actually  correct.  For  it  is 
possible  to  determine  the  time  which  elapses  between 
the  irritation  of  the  nerve  and  the  commencement 
of  muscular  pulsation.  For  this  purpose  the  same 
methods  are  applicable  a_s  we  employed  in  the  case 
of  muscles.  Electric  measurement  of  time,  or  the 
myograph  represented  in  fig.  17,  may  be  used  for  this 
purpose.  As  however  in  the  present  case  the  point  to 
be  determined  is,  not  the  form  of  the  muscle-curve, 
but  the  moment  of  its  commencement,  duBois-Eeymond 
simplified  the  apparatus  so  that  the  curve  is  draAvn  on 
a  flat  plate,  which  is  pushed  forward  by  spring  power. 
Fig.  28  represents  the  apparatus.  It  stands  on  a  strong 
cast-iron  stand  from  which  rise  the  two  massive  brass 
standards  A  and  B.  A  light  brass  frame  carries  the 
indicating  plate,  which  is  of  polished  looking-glass, 
1  GO  mm.  in  length  by  50  mm.  in  breadth.  The  frame  runs 
with  the  least  possible  amount  of  friction  on  two  parallel 
steel  wires  stretched  between  the  standards.  The  dis- 
tance between  the  standards  is  equal  to  twice  the  length 
of  the  frame,  so  that  the  whole  length  of  the  plate  passes 
across  the  indicating  pencil  when  the  frame  is  pushed 
from  standard  to  standard.  Eound  steel  rods  are  fastened 
to  the  short  sides  of  the  frame ;  and  these  rods  in  length 
somewhat  exceed  the  path  along  which  the  frame  passes, 
and  they  then  pass,  with  as  little  friction  as  possible, 
through  holes  in  the  standards  A  and  B.  The  end  b  of 
one  of  these  rods  is  surrounded  by  a  steel  spring.  By 
compressing  this  between  the  standard  B  and  a  knob  on 


112  PHYSIOLOGY    OF    MUSCLES   AND    NERVES. 

the  end  of  the  rod,  and  thus  driving-  the  frame  witti  the 
rods  from  B  to  A,  in  a  direction  opposite  to  that  of  the 
arrow  on  the  indicating  phite,  a  point  is  reached  at 
which  the  '  trigger '  which  is  seen  on  the  standard  ^, 
and  which  acts  upward,  fits  into  a  corresponding  notch 
in  the  rod  at  a,  thus  preventing  the  re-extension  of  the 
spring.     It  therefore  remains  compressed  till  pressure 


Fig.  28.    Spring  Myograph,  as  used  by  du  Bois-Reymond. 

on  the  trigger  frees  the  frame,  which  then  traverses  the 
whole  length  of  the  wires  at  a  speed  depending  on  the 
strength  of  the  spring,  &c.,  in  the  direction  from  A  to  B, 
that  indicated  by  the  arrow. 

In  order  to  describe  the  miiscle-pulsation  on  this 
plate,  side  by  side  with  it  there  is  a  lever  with  an 
indicating  pencil,  such  as  was  used  in  the  former  ex- 
periment, to  indicate  the  height  of  muscular  elevation 


TRANSMISSION   OF   THE   EXCITEMENT.  113 

and  the  elastic  extension  (see  fig.  8,  p.  26).  This  part 
is  omitted  in  fig.  28,  in  order  to  make  the  indicating 
plate  more  visible.  The  rate  at  which  the  plate  flies 
from  A  to  B  at  first  increases  up  to  the  point  at  which 
the  spring  exceeds  the  position  in  which  it  was  when  at 
rest.  When  the  frame  is  in  the  position  corresponding 
with  this  point,  a  projection  d,  which  is  situated  on  the 
lower  edge  of  the  frame,  strikes  the  lever  h  and  thus 
opens  the  main  current  of  an  inductorium,  by  which  an 
inductive  cm'rent  is  caused  in  the  secondary  coil  of  the 
inductorium ;  and  this  traverses  and  irritates  the  muscle. 
The  result  of  this  is  that  the  muscle  is  irritated  exactly 
at  the  moment  at  which  the  glass  plate  assumes  a 
definite  position  relatively  to  the  indicating  pencil  of 
the  lever.  If  the  glass  plate  is  first  pushed  toward  A,  and 
is  then  slowly  pushed  toward  5,  until  the  projection  d 
just  touches  the  lever,  and  if  the  muscle  is  then  caused 
to  pulsate,  the  indicating  pencil,  being  raised  by  the 
pulsation,  describes  a  vertical  line,  the  height  of  which 
represents  the  height  of  elevation  of  the  muscle.  If 
the  glass  plate  is  agajn  brought  back  to  A,  and,  by 
pressing  the  trigger,  is  then  caused  to  fly  suddenly  and 
with  great  speed  toward  B,  then  the  irritation  of  the 
muscle  will  occur  when  the  glass  plate  is  in  exactly  the 
same  position,  the  indicating  pencil  standing  exactly 
at  the  vertical  stroke  before  described.  The  muscular 
pulsation  thus  produced  will,  however,  in  this  case  be 
indicated  on  the  rapidly  moving  glass  plate,  with  the 
result  of  giving,  not  a  simple  vertical  stroke,  but  a 
curved  line.  The  distance  of  the  point  of  commence- 
ment from  the  vertical  stroke  expresses  the  latent 
irritation. 

If,  instead  of  irritating  the  muscle  itself,  a  point 


114  PHYSIOLOGY    OF    MUSCLES   AND    NERVES.  ' 

in  the  uerve  is  exposed  to  the  irritation,  the  muscle  in 
this  case  also  describes  the  curve  of  its  pulsation  on 
the  rapidly  moved  plate  of  the  myograph.  Arranging 
matters  so  that  two  curves  of  pulsation  are  allowed 
to  describe  themselves  in  immediate  sequence,  but  with 
the  difference  that  the  nerve  is  irritated  in  one  case  at 
a  point  near  the  muscle,  but  in  the  other  case  at  a 
point  far  from  the  muscle,  two  curves  will  be  obtained 
on  the  plate  of  the  myograph,  which  will  appear  ex- 
actly alike  but  yet  will  not  cover  each  other.  On  the 
contrary,  they  are  everywhere  somewhat  separated 
from  each  other,  as  is  shown  in  figure  29.^     In  this 


0 

Fig.  29.     Pi;opagation  of  the  excitement  within  nehves. 

figure,  a  6  c  is  the  curve  first  described,  on  irritation 
of  the  nearer  portion  of  the  nerve ;  in  order  to  dis- 
tinguish it  from  the  other  it  is  marked  by  small  nicks ; 
a'  h'  c'  represents  the  curve  indicated  immediately  after 
the  former,  but  obtained  as  the  result  of  the  irritation 
of  a  portion  of  the  nerve  remote  from  the  muscle.  The 
second  curve  is  seen  to  be  somewhat  separated  from  the 
other ;  it  does  not  commence  so  soon  after  the  moment 
of  irritation  (which  is  indicated  by  the  vertical  stroke  o) ; 
that  is,  a  longer  time  elapsed  between  the  moment  of 

'  The  curves  in  fig.  29  wore  described  when  the  g]ass  plate 
moved  more  rapid! j'-.  so  that  they  appear  more  extended  than  those 
represented  in  figure  18. 


TKAKSMISSION    OF   THE   EXCITEMENT.  115 

irritation  and  the  pulsation  of  the  muscle  in  the  latter 
case  than  in  the  former ;  and  this  diflference  evidently 
depends  only  on  the  fact  that  in  the  latter  case  the 
excitement  within  the  nerve  had  to  traverse  a  longer 
distance,  and  therefore  reached  the  muscle  later,  so 
that  the  pulsation  did  not  begin  till. later. 

This  time  may  be  measured,  if  the  rate  at  which 
the  plate  moved  is  known ;  or  if  simultaneously  with 
the  muscle-pulsation  the  vibrations  of  a  tuning-fork 
are  allowed  to  indicate  themselves  on  the  plate.  From 
the  time  thus  found  and  from  the  known  distance 
between  the  two  irritated  points  of  the  nerve,  the  rate 
at  which  the  excitement  propagates  itself  along  the 
nerve  may  be  calculated.  Helmholtz,  on  the  ground 
of  his  experiments  with  the  nerves  of  frogs,  found  it  to 
be  about  24  m.  per  second.  It  is  not,  however,  quite 
constant,  but  varies  with  the  temperature,  being  greater 
in  higher  and  less  in  lower  temperatiu-es.  It  has  also 
been  determined  in  the  case  of  man.  If  the  wires  of 
the  inductive  apparatus  are  placed  on  the  uninjured 
human  skin,  it  is  possible,  as  the  skin  is  not  an  isolator, 
to  excite  the  underlying  nerves,  especially  where  they 
are  superficially  situated.  On  thus  irritating  two  points 
in  the  course  of  the  same  nerve,  the  resulting  pheno- 
mena are  exactly  the  same  as  those  just  observed  in  the 
case  of  the  nerves  of  frogs.  In  order  to  determine  the 
commencement  of  the  muscle  pulsation  in  the  un- 
injured human  muscle,  a  light  lever  is  placed  on  the 
muscle  in  such  a  way  that  it  is  raised  by  the  thickening 
of  the  latter.  Experiments  of  this  kind  were  made  by 
Helmholtz  with  the  muscles  of  the  thumb.  The  appro- 
priate nerve  (n.  rtiedianus)  may  be  irritated  near  the 
wrist  and  near  the  elbow.    From  the  resultinfy  difference 


J 16  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

in  time  and  from  the  distance  between  the  two  irritated 
points  the  rate  of  propagation  of  the  excitement  was 
found  to  be  30  m.  per  second.  The  high  figure  as  com- 
pared with  that  found  with  the  nerves  of  frogs  is  ex- 
plained by  the  higher  temperature  of  human  nerves. 
The  rate  of  propagation  would  indeed  be  much  lowered 
if  the  temperature  of  the  arm  were  considerably  de- 
creased by  the  use  of  ice. 

The  above  calculation  of  the  rate  of  propagation  is 
made  on  the  assumption  that  this  rate  is  constant 
throughout  its  duration.  There  is,  however,  nothing 
to  shoAV  that  this  is  the  case.  On  the  contrary,  it  is 
more  probable  that  the  propagation  proceeds  at  first  at 
a  greater  and  afterwards  at  a  less  speed.  This  may  be 
inferred  from  an  experiment  arranged  by  H.  Munk.  If 
three  pairs  of  wires  are  applied  to  a  long  nerve,  one 
close  to  the  muscle,  another  at  the  centre,  and  the 
third  considerably  above,  and  then  causing  three  con- 
secutive curves  to  describe  themselves  on  the  myo- 
graph plate  by  irritating  these  three  points,  it  will 
be  found  that  the  three  curves  are  not  equally  removed 
from  each  other ;  on  the  contrary,  the  first  and  second 
stand  very  near  together,  while  the  third  is  far  from 
the  two  former.  More  than  double  the  time  was  re- 
quired for  the  excitement  to  traverse  the  full  distance 
from  the  upper  to  the  lower  end  than  it  took  to  traverse 
the  half-distance  from  the  middle  of  the  nerve  to  its 
lower  end.  The  simplest  explanation  which  can  be 
given  of  this  phenomenon  is  that  the  excitement  during 
its  propagation  is  gradually  retarded,  just  as  a  billiard  ball 
moves  at  first  very  quickly  but  afterward  at  a  gradually 
decreasing  speed.  The  retardation  of  the  billiard  ball 
is  due  to  the  friction  of  the  underljdng  surface.     From 


ISOLATED   TRANS]VUSSION.  117 

this  it  may  be  inferred  that  a  resistance  to  the  trans- 
mission exists  within  the  nerve,  and  that  this  gradually 
retards  the  rate  of  propagation.  Such  a  resistance  to 
transmission  is  also  probable  on  certain  other  grounds, 
to  which  subject  we  shall  presently  revert. 

4.  If  the  main  stem  of  a  nerve  is  irritated  by  elec- 
tric shocks,  all  the  fibres  are  invariably  simultaneously 
irritated.  On  tracing  the  sciatic  nerve  to  its  point  of 
escape  from  the  vertebral  column,  it  appears  that  it  is 
there  composed  of  four  distinct  branches,  the  so-called 
roots  of  the  sciatic  plexus.  These  rootlets  may  be 
separately  irritated,  and  when  this  is  done  contractions 
result,  which  do  not,  however,  affect  the  whole  leg  but 
only  separate  muscles,  and  different  muscles  according 
to  which  of  the  roots  is  irritated.  Now  as  the  fibres 
contained  in  the  root  afterward  coalesce  in  the  sciatic 
nerve  within  a  membrane,  it  follows  from  the  experi- 
ment just  described  that  the  irritation  yet  remains 
isolated  in  the  separate  fibres  and  is  not  imparted  to 
the  neighbouring  fibres.  This  statement  holds  good  of 
all  peripheric  nerves.  Wherever  it  is  possible  to  irri- 
tate separate  fibres  the  irritation  is  always  confined  to 
these  fibres  and  is  not  transmitted  to  those  adja- 
cent. We  shall  afterwards  find  that  such  transmis- 
sions from  one  fibre  to  another  occur  within  the  cen- 
tral organs  of  the  nervous  system.  But  in  these  cases 
it  can  be  shown  with  great  probability  that  the  fibres 
not  only  lie  side  by  side,  but  that  they  are  in  some 
way  interconnected  by  their  processes.  In  peripheric 
nerve-fibres  the  irritation  always  remains  isolated. 
Their  action  is  like  that  of  electric  wires  enclosed  in 
insulating  sheaths.  One  of  these  nerves  may  indeed 
be  compared  to  a  bundle  of  telegraph  wires,  which  are 


118  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

protected  from  direct  contact  with  each  other  by  gutta- 
percha or  by  some  other  substance.  The  comparison 
is,  however,  but  superficial.  No  electrically-isolating 
membrane  can.  really  be  discovered  in  any  part  of  the 
nerve-fibre,  but  all  their  parts  conduct  electricity. 
When,  as  we  shall  presently  find,  electric  processes 
occur  within  the  nerve,  these  standing  in  definite  re- 
lation to  the  activity  of  the  nerves,  we  must  assume  that 
isolation  as  it  occurs  in  the  nerves  is  not  the  same  as 
in  telegraph  wires.  We  cannot  here  trace  the  matter 
further,  but  must  accept  the  fact  of  isolated  conduction 
as  such,  reserving  its  explanation  for  a  future  occasion. 
5.  On  irritating  the  nerves  by  means  of  currents 
from  an  inductive  apparatus,  it  is  found  that  the  pulsa- 
tions which  occur  are  sometimes  strong,  sometimes 
weak.  All  nerves  are  not  alike  in  this  respect,  and 
even  the  parts  of  one  and  the  same  nerve  are  often 
very  different.  We  must  accordingly  suppose  that 
nerves  are  variable  in  the  degree  in  which  they  receive 
irritation.  This  is  spoken  of  as  the  excitability  of  the 
nerve,  to  express  the  greater  or  less  ease  with  which 
they  may  be  put  in  action  by  external  irritation.  Two 
ways  may  be  adopted  to  measure  the  excitability  of  a 
nerve  or  of  a  certain  point  in  a  nerve.  Either  the 
same  irritant  may  always  be  used,  and  the  excitability 
may  be  determined  by  the  strength  of  the  muscular 
pulsation  evoked  by  this  irritant ;  or  the  irritant  may 
be  altered  until  it  just  suffices  to  evoke  a  muscular 
pulsation  of  a  definite  strength.  In  the  former  case 
it  is  evident  that  the  excitability  must  be  estimated 
as  higher  in  proportion  as  the  muscular  pulsation  pro- 
duced by  the  irritant  is  stronger;  in  the  latter  case 
the    excitability  is    said  to   be   greater   in   proportion 


EXCITABILITY.  119 

as  the  irritant  wHch  is  able  to  evoke  a  pulsation  of 
definite  strength  is  weaker.  Each  of  these  methods 
when  practically  applied  has  advantages  and  disad- 
vantages. The  former  is  capable  of  detecting  very 
minute  differences  in  the  excitability,  but  it  can  only 
do  this  within  certain  narrow  limits;  for  when  the 
excitability  sinks,  the  limit  for  a  definite  irritant  is 
soon  reached,  after  which  no  further  pulsation  at  all 
results ;  and  when  the  excitability  rises,  the  muscle 
attains  its  maximum  contraction,  above  which  it  is 
incaj)able  of  fiuther  contraction.  Changes  above  or 
below  either  of  these  limits  are,  therefore,  beyond 
observation  so  long  as  the  irritant  remains  the  same. 
The  best  way  to  apply  the  second  method  practically  is 
to  find  that  strength  of  irritant  which  exactly  suffices 
to  produce  a  just  observable  contraction  of  the  muscle. 
This  assumes  the  power  of  graduating  the  strength  of 
the  irritant  at  pleasure.  If  inductive,  currents  are  used 
to  effect  irritation,  this  graduation  may  be  made  with 
the  greatest  precision  by  altering  the  distance  between 
the  primary  and  secondary  coils  of  the  apparatus.  In 
du  Bois-Eeymond's  sliding  inductive  apparatus,  repre- 
sented in  fig.  13,  p.  35,  the  secondary  coil  is,  there- 
fore, attached  to  a  slide  which  may  be  moved  forward 
in  a  long  groove.  This  arrangement  is  used  in  order 
to  find  the  particular  distance  of  the  secondary  coil 
from  the  primary  which  results  in  a  just  observable 
contraction  of  the  muscle  ;  and  this  distance,  which 
can  be  measured  by  means  of  a  scale  divided  into 
millimetres,  is  regarded  as  the  measure  of  excitability.' 
6.  If  a  recently  prepared  nerve,  as  fresh  as  possible, 
is  placed  on  a  series  of  pairs  of  wires,  and  the  excita- 
'  See  Notes  and  Additions,  No.  3. 


120     PHYSIOLOGY  OF  MUSCLES  AND  NEEVES. 

bility  at  the  various  points  of  the  nerve  is  consecutively 
determined  in  the  way  described  above,  it  is  generally 
found  that  the  excitability  of  the  upper  part  of  the 
nerve  is  greater  than  that  of  the  lower.  There  is,  how- 
ever, no  great  regularity  in  this  character.  Sometimes  a 
point  is  found  in  the  centre  of  the  nerve  which  is  less 
irritable  than  those  immediately  above  and  below  it. 
Very  frequently  the  most  excitable  point  occurs,  not 
immediately  at  the  cut  end,  but  at  some  little  distance 
from  this ;  so  that,  on  proceeding  downward,  it  is  found 
to  increase  at  first,  and  then,  at  a  yet  lower  point,  to 
decrease  again.  If  such  a  nerve  is  observed  for  some, 
little  time,  its  excitability  at  the  various  points  being 
tested  every  five  minutes,  it  is  found  that  the  excita- 
bility alters  especially  soon  at  the  upper  end;  it  de- 
creases, and  in  a  short  time  is  entirely  extinguished,  so 
that  no  muscular  pulsations  can  afterwards  be  elicited 
from  the  upper  parts  even  by  the  most  powerful 
currents.  The  nerve  is  then  said  to  be  dead  in  its 
upper  parts,  and  this  death  proceeds  gradually  down- 
ward in  the  nerve,  so  that  pulsations  can  only  be 
obtained  by  irritating  the  part  situated  nearest  the 
muscle,  and  at  a  little  later  period  even  this  part 
becomes  dead.  After  the  whole  nerve  is  dead,  pul- 
sations may  yet  always  be  obtained  for  a  time  by 
direct  irritation  of  the  muscle.  The  muscle  does  not 
usually  die  until  much  later  than  the  nerve  Yet  in  a 
quite  fresh  preparation  of  the  nerve  and  muscle,  the 
latter  is  always  less  excitable  than  the  former,  and 
a  much  stronger  irritant  is  required  to  excite  the 
mascle  directly,  than  indirectly  through  the  nerve. 
In  all  these  experiments  the  nerve  must  be  care- 
fully protected  from  drying  up,  as  otherwise  its  excita- 


CURVE    OF    EXCITABILITY.  121 

bility  is  very  soon  destroyed,  and  in  a  very  irregular 
manner. 

We  have  seen  that  the  nerve  dies  gradually  fiom 
the  top  downward.  This  death  does  not,  however, 
consist  in  a  simple  falling  off  in  the  excitability  from 
its  original  degree  till  it  completely  dies  out.  If  the 
excitability  is  tested  from  time  to  time  at  a  point  some 
distance  from  the  cut  end,  it  is  found  to  increase  at 
first  until  it  reaches  a  maximum,  at  which  it  remains 
for  some  time  stationary,  and  it  is  not  till  after  this 
that  it  gradually  decreases  and  finally  expires.  The 
further  the  point  experimented  on  is  from  the  point 
which  has  been  cut,  the  more  slowly  do  all  these 
changes  occur ;  but  their  sequence  is  in  all  cases  essen- 
tially alike.  The  explanation  of  this  may  be  that  the 
upper  parts  of  the  nerve,  which  directly  after  the  pre- 
paration is  made  usually  exhibit  the  highest  degree 
of  excitability,  are  really  already  changed.  It  must  be 
assumed  that  these  changes  intervene  very  quickly  at  a 
point  close  to  the  section,  so  that  it  is  impossible  to 
submit  these  points  to  observation  until  they  are  al- 
ready in  the  condition  which  does  not  intervene  till 
later  at  the  lower  points — in  the  condition,  that  is,  of 
increased  excitability.  This  view  is  confirmed  by  the 
following  experiment :  if  the  excitability  is  determined 
at  a  lower  point  of  the  nerve,  and  the  latter  is  then  cut 
through  above  this  point,  the  excitability  increases  at 
the  point  tested,  and  this  takes  place  more  quickly  in 
proportion  as  the  cut  was  made  nearer  to  the  tested 
spot.  Each  of  the  lower  points  may,  therefore,  be 
artificially  brought  under  the  same  conditions  under 
which  only  the  upper  parts  of  the  nerve  usually  lie, 
that   is,  it  may  be  arranged  that  they  are   near  the 


122     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

point  of  section.  These  chang-es  in  the  excitability 
may,  therefore,  he  thus  conceived :  that  when  the 
nerve  is  cut  some  influence  makes  itself  felt  from  this 
cut,  and  that  this  first  increases  the  excitability  of  the 
nerve,  then  decreases,  and  then  extinguishes  it.  If 
this  view  is  right,  we  must  assume  that  the  high 
degree  of  excitability  of  a  freshly  cut  nerve  is  also 
only  the  result  of  the  incision  which  is  made.  This  is 
not,  however,  exactly  the  case.  The  nerve  with  the 
muscle  of  a  living  frog  may  be  freed  and  prepared  np 
to  the  vertebral  column  without  separating  it  from  the 
dorsal  marrow.  On  irritating  the  various  points  in  such 
a  nerve,  differences,  slight  indeed  but  yet  observable, 
are  noticed  in  the  excitabiKty,  the  upper  parts  being 
always  more  excitable  than  the  lower.  Uniujured 
human  nerves  may  also,  as  we  have  seen,  be  irritated 
at  various  points  in  their  course,  and  in  this  case  also 
it  is  found  that  irritation  is  invariably  more  easily  effec- 
tive in  the  upper  than  in  the  lower  parts. 

Pfliiger,  who  first  called  attention  to  the  differences 
of  excitability  at  the  various  points  of  the  nerve,  thought 
that  the  explanation  of  this  is  that  the  irritation  evoked 
at  one  point  in  the  nerve,  in  propagating  itself  along 
the  nerve,  gradually  increases  in  strength;  he  spoke 
of  it  as  an  avalanche-like  increase  in  the  exciternent 
tvithin  the  nerves.  This  explanation  appears  to  contra- 
dict the  above-mentioned  fact  as  to  the  effect  of  cutting 
on  the  nerve,  for  in  such  cases  it  appears  that  the  irri- 
tation is  strengthened  by  the  cutting  away  of  the 
higher  portion  of  the  nerve,  even  though  the  length  of 
that  portion  of  the  nerve  which  is  traversed  by  the 
irritation  remains  unaltered.  It  must  at  any  rate  be 
admitted  that  at  one  and  the  same  point  in  the  nerve 


DEATH    OF   THE    ISERVE.  123 

the  excitability  may  vary  in  degree,  and  it  is  therefore 
simpler  to  assume  that  the  difference  in  the  results  of 
irritating  the  nerve  at  various  points  depends  directly 
on  differences  in  the  excitability  at  those  points,  instead 
of  being  in  the  first  place  dependent  on  changes  caused 
by  transmission ;  it  can  even  be  shown  to  be  probable 
on  various  grounds,  as  indicated  above,  that  the  excite- 
ment in  propagating  itself  through  the  nerve  meets 
with  resistance,  and  is  therefore  rather  weakened  than 
strengthened.  Why  the  excitabihty  diflfers  in  different 
parts  of  the  same  nerve  we  cannot  explain.  As  long 
as  we  are  ignorant  of  the  inner  mechanism  of  nerve- 
excitement,  we  must  be  satisfied  to  collect  facts  and  to 
draw  attention  as  far  as  may  be  to  the  connection  of 
details,  but  we  must  decline  to  offer  a  full  explanation 
of  these.^ 

7.  The  phenomena  of  exhaustion  and  recovery  may 
be  exhibited  in  nerves  as  in  muscles.  If  a  single 
point  in  a  nerve  is  frequently  irritated,  the  actions 
become  weaker  after  a  time,  and  finally  cease  entirely. 
If  the  nerve  is  then  allowed  to  rest  for  a  time,  new 
pulsations  may  again  be  elicited  from  the  same  point. 
It  is  not  known  whether  this  exhaustion  and  recovery 
corresponds  with  chemical  changes  in  the  nerve.  We 
are  almost  entirely  ignorant  of  the  whole  subject  of 
chemical  changes  within  the  nerve.  Some  observers 
maintain  that  in  the  nerve,  as  in  the  muscle,  an  acid 
is  set  free  duriug  the  active  condition,  but  this  is 
denied  by  others.  The  generation  of  warmth  in  the 
nerve  during  its  activity  has  also  been  asserted,  but 
this  is  also  doubtful.  If  any  chemical  changes  do  take 
place  within  the  nerve,  they  are  extremely  weak  and 
'  See  Notes  and  Additions,  No.  4. 


124  Pm'SlOLOGrY    OF   MUSCLES   AND   NERVES. 

cannot  be  shown  with  our  present  appliances.  As 
motions  of  the  smallest  particles  (molecules)  probably 
take  place  in  the  nerve,  though  the  external  form 
remains  unaltered,  and  therefore  no  work  worthy  of 
consideration  is  accomplished,  it  is  easily  intelligible 
that  these  processes  may  be  accompanied  only  by  ex- 
tremely slight  changes  in  the  constituent  parts. 

The  speed  with  which  death  and  the  changes  in 
excitability  connected  with  death  take  place  mainly 
depends,  apart  from  the  length  of  the  nerve,  on  the 
temperature.  The  higher  the  temperature  the  more 
quickly  does  the  nerve  die.  At  a  temperature  of  44°  C. 
death  occurs  in  from  ten  to  fifteen  minutes ;  at  75°  C. 
in  a  few  seconds  ;  and  in  the  average  temperature  of  a 
room  the  lower  ends  of  a  long  sciatic  nerve  may  re- 
tain their  excitability  for  twenty-four  hours  or  longer 
after  extraction  and  preparation.  Drying  at  first  in- 
creases the  excitability,  but  afterwards  rapidly  decreases 
it.  Chemical  agents,  such  as  acids,  alkalis  and  salts, 
destroy  the  excitability  the  more  rapidly  the  more 
concentrated  they  are.  In  distilled  water  the  nerve 
swells  and  rapidly  becomes  incapable  of  excitement. 
There  are,  therefore,  certain  densities  of  salt  solutions 
in  which  the  nerve  remains  excitable  longer  than  in 
thinner  or  in  more  dense  solutions.  A  solution  of  com- 
mon salt  of  0'6  to  1  per  cent.,  for  instance,  has  almost 
no  effect  on  a  nerve  submerged  in  it,  and  preserves  the 
excitability  of  this  nerve  about  as  long  as  damp  air. 
Pure  olive  oil,  if  not  acid,  may  also  be  regarded  as 
innocuous.  These  are,  therefore,  used  when  the  in- 
fluence of  different  temperatures  on  the  nerve  is  to  be 
studied. 


CHAPTER  VIII. 

I  Electrotonus  ;  2,  ilodifications  of  excitability  :  3.  Law  of  pulsa- 
tions ;  4.  Connection  of  electrotonus  with  excitability;  5.  Trans- 
mission of  excitability  in  electrotonus;  6.  Explanation  of  the 
law  of  pulsations  ;  7.  General  law  of  nerve-excitement. 

1.  It  has  already  been  observed  that  a  constant  elec- 
tric current,  if  transmitted  through  the  nerve,  is  able 
to  excite  the  latter ;  but  that  this  exciting-  influence 
takes  eifect  especially  at  the  moment  at  which  the  cur- 
rent is  closed  and  opened,  and  that  it  is  less  effective 
during  the  course  of  the  current's  duration.  As  yet  it 
has  been  desirable  for  our  purpose,  that  of  studying  the 
process  of  excitement  in  nerves,  to  make  use  of  induc- 
tive currents,  which  are  of  such  short  duration  that  the 
closing  and  the  opening,  the  beginning  and  the  end, 
immediately  follow  each  other  in  quick  succession. 
Without  now  entering  into  the  question,  to  be  dis- 
cussed later,  as  to  why  the  exciting  action  of  the  cur- 
rent is  less  during  the  steady  flow  of  the  latter  than  at 
the  moments  of  closing  and  opening,  we  will  now  ex- 
amine whether  the  electric  currents  which  traverse  the 
nerves  do  not  act  on  the  nerves  in  some  other  way, 
distinct  from  their  exciting  influence. 

Let  us  suppose  that  the  current  traverses  either  the 
whole  or  a  portion  of  a  nerve.  At  the  instant  at  which 
the  current  in  the  nerve  is  closed,  the  appropriate  muscle 


126  THYSIOLOGY    OF   MUSCLES   AND   NERVES. 

pulsates,  thus  indicating  that  something,  which  we  have 
called  excitement,  has  occurred  within  the  nerve.  WTiile, 
however,  the  current  flows  steadily  through  the  nerve, 
the  muscle  remains  perfectly  quiescent,  nor  is  any 
change  apparent  in  the  nerve  itself.  Yet  it  may  easily 
be  proved  that  the  electric  current  has  effected  a  com- 
plete change  in  the  nerve,  not  only  in  that  part  traversed 
by  the  current,  but  also  in  the  neighbouring  parts  above 
and  below  the  portion  of  the  nerve  subjected  to  the 
electric  cm-rent.  The  great  importance  of  this  Kes  in 
the  fact  that  it  reveals  relations  between  the  forces 
prevailing  in  the  nerves  and  the  processes  of  the  elec- 
tric currents,  which  relations  are  of  great  importance  in 
the  explanation  of  the  activity  of  nerves. 

Our  knowledge  of  nerves  has  not  as  yet  reached 
a  point  at  which  it  is  possible  to  understand  all  the 
changes  which  occur  within  them  under  the  influence 
of  electric  currents.  Indeed,  but  one  set  of  these  changes 
can  as  yet  be  described :  these  are  the  changes  in  the 
excitability.  Of  all  the  vital  phenomena  of  nerves,  their 
capacity  of  being  brought  into  an  active  condition  by 
irritants  has  at  present  alone  been  studied  by  us.  This, 
as  has  been  said  in  the  previous  chapter,  may  be  quan- 
titatively determined.  Experiment  shows  that  the  ex- 
citability may  be  altered  by  electric  currents.  If  a 
small  portion  of  a  nerve  is  placed  on  two  wires  in  such 
a  way  that  an  electric  current  may  be  caused  to  traverse 
this  portion,  it  appears  that  not  only  the  portion  actually 
traversed  by  the  current,  but  the  nerve  beyond  this, 
also  suffers  changes  in  its  excitability.  In  order  to 
study  these,  let  us  imagine  several  pairs  of  wires  ap- 
plied to  the  nerve  n  oi'  (fig.  30).  Through  one  of 
these  pairs   of  wires,   c  d,  let  a   constant  current  be 


ELECTROTONUS. 


127 


"conducted  ;  by  means  of  proper  apparatus  the  current 
may  be  strengthened  or  weakened,  and  may  be  closed 
and  interrupted  by  means  of  a  key  at  s.  Let  a  current 
from  a  sliding  inductive  apparatus  pass  through  another 
portion  of  the  nerve,  e.g.  a  h,  and  let  us  find  that  posi- 
tion of  the  secondary  coil  at  which  the  muscle  exhibits 
marked  pulsations  of  medium  strength.  The  changes 
which  occur  in  these  pulsations  when  the  current  in 
the  portion  c  d  is  alternately  closed  and  interrupted 


Fig.  30.    Electrotoxls. 


must  now  be  observed.  It  is  found  that  thepe  changes 
depend  on  the  direction  of  the  current  within  the  nerve. 
If  the  current  passes  in  the  direction  from  c  to  d,  then 
the  action  of  the  same  irritant  is  weakened  in  the  por- 
tion a  h  as  soon  as  the  current  is  closed,  but  regains  its 
former  strength  as  soon  as  the  current  is  interrupted. 
In  this  case,  therefore,  the  excitability  in  the  contiguous 
portion  a  b  was  lowered  or  hindered  by  the  influence 
of  the  constant  current  traversing  the  portion  c  d.  If, 
however,  the  constant  current  is  reversed,  so  that  it 


128     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

passes  from  d  to  c,  the  influence  of  the  irritant  seems, 
on  the  contrary,  to  increase  in  a  b  when  the  current  is 
closed,  and  to  resume  its  original  strength  "when  the 
current  is  interrupted.  In  this  case,  therefore,  it  ap- 
pears that  the  action  of  the  current  tends  to  increase 
the  excitability.  If  the  wires  e  f  are  next  connected 
with  the  secondary  coil  of  the  inductive  apparatus,  and 
if  the  irritants  are  again  applied  in  such  a  way  that 
weak  but  noticeable  pulsations  occur,  these  latter  are 
strengthened  when  the  current  in  the  portion  c  d  passes 
from  c  to  d;  and  are,  on  the  contrary,  weakened  when 
the  current  is  in  the  opposite  direction.  In  these  two 
series  of  experiments  the  irritant  was  applied  in  one 
case  above,  in  the  other  case  below,  the  constant  cur- 
rent. Both  cases  showed  consistent  results.  As  soon, 
that  is,  as  the  irritant  acted  on  the  side  of  the  positive 
electrode  or  the  anode,  through  which  the  current 
entered  the  nerve,  the  excirability  was  in  both  cases 
lowered.  But  when  the  irritant  was  applied  on  the 
side  of  the  negative  electrode  or  the  kathode,  through 
which  the  current  emerged  from  the  nerve,  the  irritant 
being  strengthened,  the  excitability  increased. 

These  changes  in  the  excitabihty  may  be  shown 
throughout  the  whole  length  of  the  nerve;  but  they 
are  strongest  in  the  immediate  neighbourhood  of  the 
portion  traversed  by  the  constant  current,  gradually 
decreasing  upward  and  downward  from  the  electrodes. 
In  order  to  find  whether  a  change  in  the  excitability 
also  occurs  within  the  electrodes,  the  current  must  be 
made  to  traverse  a  longer  portion  of  the  nerve,  and  the 
irritant  must  then  be  applied  to  a  point  within  the 
electrodes.  According  to  the  point  at  which  the  elec- 
trode is  applied, various  changes  maybe  shown  to  occur 


ELECTROTONUS  129 

here  also.  If  the  irritant  is  near  the  positive  electrode, 
the  excitability  is  lowered ;  near  the  negative  electrode 
it  is  increased ;  and  between  the  two  occurs  a  point  at 
which  no  noticeable  change  in  the  excitabiUty  takes 
place  under  the  influence  of  the  constant  current. 

From  all  these  experiments  we  may  infer  that  a 
nerve,  one  part  of  the.  length  of  which  is  traversed  by  a 
constant  current,  passes  throughout  its  whole  length 
into  an  altered  condition,  and  that  this  is  expressed  in 
the  excitability.  One  part  of  the  nerve,  that  on  the 
side  of  the  positive  electrode,  exhibits  decreased  excita- 
bility ;  the  part  of  the  nerve  corresponding  with  the 
negative  electrode  exhibits  increased  excitabiHty.  This 
altered  condition  is  spoken  of  as  the  electrotonus  of  the 
nerve,  the  condition  which  exists  on  the  side  of  the 
anode  being  distinguished  as  anelectrotonus ;  that  on 
the  side  of  the  kathode  as  katelectrotonus.  Where  the 
anelectrotonus  approaches  the  katelectrotonus,  a  point 
occurs  between  the  electrodes  at  which  the  excitability 
remains  unchanged ;  this  is  called  the  neutral  point. 
The  neutral  point  does  not,  however,  always  lie  exactly 
between  the  electrodes  ;  but  its  position  depends  on 
the  strength  of  the  applied  currents.  When  the  cur- 
rents are  weak,  it  lies  nearer  the  anode ;  when  they 
are  stronger,  it  is  situated  nearer  the  kathode  ;  and 
when  the  currents  are  of  a  certain  medium  strength, 
the  neutral  point  is  exactly  midway  between  the  two 
electrodes. 

This  electrotonic  condition  of  the  nerve  may  be  ex- 
hibited as  in  fig.  31.  In  this  n  n'  indicates  the  nerve, 
a  and  h  the  electrodes,  a  signifying  the  anode,  h  the 
kathode.  The  direction  of  the  current  within  the  nerve 
is,  therefore,  that  indicated  by  the  arrow.  In  order  to 
7 


130 


PHYSIOLOGY   OF   MUSCLES   AND   NERVES. 


indicate  the  change  which  the  excitability  undergoes  at 
any  definite  point  in  the  nerve,  let  us  suppose  a  straight 
line  drawn  at  this  point  at  right  angles  to  the  longitu- 
dinal direction  of  the  nerve,  and  let  this  line  be  made 
longer  in  proportion  as  the  change  is  greater.  In  order, 
moreover,  to  show  that  the  changes  which  occur  toward 
the  anode  are  of  an  opposite  tendency  to  those  toward 
the  kathode,  let  the  line  on  the  anode  side  be  drawn 
downward,  that  on  the  kathode  upward.  By  connecting 
together  the  heads  of  these  lines  a  curve  is  obtained 
which  diagrammatically  represents  the  changes  at  each 


Fig.  31.    Electrotonts  under  the  influence  ok  currents  of 
varying  strexgth. 

point.  Of  the  three  curves,  the  middle  represents  the 
condition  under  the  influence  of  a  current  of  medium 
strength ;  the  other  two  curves,  indicated,  the  one  by 
short  lines,  the  other  by  a  dotted  line,  represent  the 
conditions  under  the  influence  of  a  strong  and  of  a 
weak  current  respectively.  These  curves  show  that  the 
changes  are  more  marked  in  proportion  as  the  cur- 
rent is  stronger  ;  that  they  are  most  strongly  developed 
exactly  at  the  electrode  points ;  and,  finally,  that  the 
neutral  point,  under  the  influence  of  currents  of  dif- 
ferent degrees  of  strength,  assumes  a  variable  position 
between  the  electrodes. 


MODIFICATION    OF    THE    EXCITABILITY.  131 

2.  Apart  from  these  clianges  in  the  excitability 
which  are  thus  observable  while  a  continuous  current 
passes  through  the  nerve,  others  can  also  be  shown  to 
occur  immediately  after  the  opening  of  the  current. 
Indeed,  the  excitability  altered  in  electrotonus  does  not 
immediately  revert  to  its  normal  value  when  the  cur- 
rent is  interrupted,  but  only  regains  this  after  the  lapse 
of  a  short  time.  The  duration  of  the  changes  in  the 
excitability  observable  after  the  opening  of  the  current 
is  greater  in  proportion  as  the  current  is  stronger  and 
its  duration  is  longer.  These  changes,  which,  to  dis- 
tinguish them  from  the  electrotonic  changes,  are  called 
modifications  of  the  excitability,  are  not  merely  the 
continuance  of  an  electrotonic  condition,  but  are  some- 
times completely  different  from  the  latter.  If,  for  in- 
stance, the  experiment  is  tried  at  a  point  near  the 
anode,  at  which  the  excitability  is  decreased  during  the 
continuance  of  the  current,  the  excitability  is  found 
to  be  increased  immediately  after  the  opening  of  the 
current,  and  it  is  not  till  after  this  that  the  original 
normal  excitability  is  regained.  Similai'ly,  in  the  neigh- 
bourhood of  the  kathode,  the  excitability  decreases  for 
a  short  time  after  the  opening  of  the  current,  after 
which  it  again  increases,  and  only  gradually  regains  its 
normal  condition.  As  a  rule,  these  modifications  do  not 
last  more  than  a  few  parts  of  a  second.  If,  however, 
the  constant  current  has  been  long  present  in  the  nerve, 
these  modifications  may  endure  for  a  somewhat  longer 
period.  On  account  of  their  transient  nature  it  is  diffi- 
cult to  observe  and  test  them.  The  change  of  condi- 
tion which  follows  the  opening  of  the  current  within  the 
nerve  may,  moreover,  lead  to  excitement  in  the  latter ; 
so  that,  on  the  opening  of  a  cux'rent  which  has  been 


132     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

present  in  the  nerve  for  some  time,  a  series  of  pulsa- 
tions or  an  apparent  tetanus  is  occasionally  observed. 
This  phenomenon  has  long  been  known  as  an  opening 
tetanus,  or  as  Rittefs  tetanus.  The  connection  existing 
between  these  changes  in  the  excitability,  and  the  fact 
that  the  nerve  may  be  excited  by  electric  currents,  has 
led  to  the  adoption  of  a  view  of  the  electric  excitement 
in  nerves  which  we  shall  not  be  able  to  develop  until  we 
have  more  closely  studied  electric  excitement  itself. 

3.  If  a  continuous  current  is  passed  through  a  nerve, 
and  is  alternately  closed  and  opened,  the  excitement 
appears  to  occur  irregularly,  sometimes  at  the  closing, 
sometimes  at  the  opening  of  the  current,  and  occasion- 
ally even  at  both.     Closer  observation  has,  however, 
shown  that  very  definite  laws  control  this,  provided  that 
attention  is  paid  to  the  strength  of  the  current  and  its 
direction  within  the  nerve.    Let  us  first  examine  these 
phenomena  as  they  occur  in  fresh  nerve,  and,  as  we  found 
that  the  conditions  in  the  nerve  change  very  rapidly 
in  the  neighbourhood  of  the  cut  end,  let  us  commence 
our  observations  at  a  low  point  in  a  fresh  nerve,  of 
which  as  great  a  length  as  possible  has  been  extracted. 
For  this  purpose  it  is  especially  necessary  to  possess  a 
convenient  means  of  graduating  at  will  the  strength  of 
the  applied  currents.    Various  methods  have  been  used 
for  this  prupose.     The  best  is  that  which  is  based  on 
the  distribution  of  the  currents  in  branching  conduc- 
tors.    The  electric  current,  on  being  made  to  traverse 
a  conductor   which    separates    at  any  point  into  two 
branches,  divides,  the  strength  of  the  currents  distri- 
buted into  these  two  branches  not  being  always  equal, 
but  being  in  each  branch  in  inverse  ratio  to  the  resis- 
tance offered  in  that  branch.    Supposing  that  the  nerve 


LAW    OF   PULSATIONS. 


133 


is  inserted  in  one  branch,  and  that  the  resistance  of  the 
other  branch  is  altered,  then  the  strength  of  the  cur- 
rent passing  through  the  nerve  will  change,  although 
the  conductor  which  contains  the  nerve  remains  un- 
altered ;  the  current  within  the  nerve  will  increase 
in  strength  when  the  resistance  in  the  other  branch  is 
increased,  and  it  will  decrease  when  the  resistance  in 
this  branch  is  decreased. 

The  resistance  of  a  wire  being  proportionate  to  its 
length,  it  is  only  necessary  to  arrange,  as  the  conductor 


Fig.  32.    Eheoci:oi;i). 

A  S,  a  wire  the  length  of  which  can  be  in  some  way 
altered.  The  simplest  way  of  doing  this  is  by  extend- 
ing the  wire  in  a  straight  line  and  moving  a  slidino-- 
piece  along  it,  so  that  any  required  length  of  the  wire 
may  be  brought  into  the  conductor.  Such  an  apparatus 
is  called  a  rheochord,  from  pFos,  a  current,  and  x^P^V, 
a  chord— because  the  current  is  conducted  along  a  wire 
extended  like  a  chord.  A  rheochord  of  the  simplest  kind 
is  represented  in  fig.  32.  The  current  of  the  chain 
P  Z  traverses  the  wire  A  B.     From  A  a  branch  con- 


134  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

ductor  passes  to  the  nerve,  and  returns  from  there 
to  the  shde  S,  which  sKps  along  the  wire  A  B.  The 
branch-current  traversing  the  nerve  is  strengthened  or 
weakened  according  as  this  slide  is  placed  further  from 
or  nearer  to  A. 

By  means  of  a  rheochord  of  this  sort  there  is  no 
difficulty  in  making  the  currents  within  the  nerve  so 
weak  that  they  exercise  no  influence  at  all.  If  their 
strength  is  then  gradually  increased,  a  pulsation  is 
always  first  seen  to  occiu*  in  the  fresh  nerve  when  the 
current  is  closed,  whatever  the  direction  of  the  current 
within  the  nerve.  In  order  to  be  able  to  indicate  the 
direction,  it  has  become  customary  to  speak  of  such  a 
current,  when  it  passes  within  the  nerve  from  a  central 
to  the  more  peripheric  parts,  as  descending,  and  when 
it  passes  in  the  opposite  direction,  as  ascending. 

Ascending  and  descending  currents,  therefore,  when 
they  are  weak,  afford  pulsations  only  on  the  closing 
of  the  current.  If  the  strength  of  the  current  is  in- 
creased, pulsations  gradually  begin  to  occur  also  on 
the  opening  of  the  current,  at  first  usually  with  the 
descending  current,  though,  when  the  strength  is  in- 
creased yet  more,  they  occur  in  connection  with  the 
ascending  current  also.  Finally,  the  pulsations  in  all 
four  cases  are  of  equal  strength.  If,  however,  the 
strength  of  the  current  is  yet  further  increased,  two 
of  these  four  pulsations  again  become  weaker — the 
closing  pulsation  with  the  ascending  current,  and  the 
opening  pulsation  with  the  descending  current.  A 
strength  of  current  is  at  last  reached  at  which  these 
two  pulsations  entirely  cease,  so  that  pulsations  occur 
only  on  the  closing  of  the  descending,  and  on  the 
opening  of  the  ascending  cuiTents.    These  phenomena, 


LAW   OF   PULSATIONS. 


135 


which  represent  the  dependence  of  the  excitement  of 
the  nerve  on  the  strength  and  direction  of  the  current, 
are  spoken  of  as  the  law  of  pulsations.  This  law  is 
represented  in  the  following  table,  in  which  S  signifies 
closing,  0  opening,  Z  pulsation,  and  E  rest — i.e.  no 
pulsation — the  duration  of  the  currents  being  indicated 
by  the  arrows. 

Law  op  Pulsations  in  the  case  op  Fkksh  Neeve. 


Current  Weak 

Current  of  Medium 
strength 

Current  Strong 

1 

a,  Z             0,  E, 

S,  Z            0,  z 

S,  Z             0,  R 

t 

y,  z          0,  R 

S,  Z            0,  z 

S,  R             0,  Z 

As  soon  as  the  nerve  dies,  the  phenomena  under 
the  law  of  pulsations  change.  If  weak  currents  are 
applied  to  a  fresh  nerve,  which  in  either  direction 
produce  pulsations  only  on  the  closing  of  the  current, 
and  if  then,  the  currents  remaining  entirely  unaltered, 
their  influence  on  the  nerve  is  tested  from  time  to 
time,  it  will  be  found  that  pulsations  gradually  begin 
to  occur  on  the  opening  of  the  current;  these  are  at 
first  weak,  but  they  continually  become  stronger  till 
they  are  fully  equal  in  strength  to  the  pulsations 
resulting  on  the  closing  of  the  current.  This  condi- 
tion is  retained  for  some  time,  after  which  the  closing 
pulsations  of  the  ascending  current  and  the  opening 
pulsations  of  the  descending  current  become  weaker, 
and  finally  entirely  disappear,  so  that  the  descending 
current  produces  only  closing  pulsations,  and  the 
ascending  current  only  opening  pulsations ;  and  this 
condition  endures  until  the  excitability  at  the  points 
examined    is    entirely    expended,    the    pulsations    be- 


136     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

coming  gradually  weaker,  and  finally  disappearing  en- 
tirely. The  law  of  pulsations  in  the  case  of  dying 
nerve  may  also  be  represented  in  tabular  form,  three 
stages  of  excitability  being  distinguished ;  the  signs 
remain  the  same  as  in  the  former  table. 

Law  op  Pulsations  in  the  case  op  Dying  Nerve. 
(Under  the  Application  of  Weak  Currents.) 


First  Stage 

Second  Stage 

Third  Stage 

i 

S,  Z              0,  R 

S,  Z            0,  z 

S,  Z              0,  R 

t 

S,  Z              0,  R 

S,  Z             0,  z 

S,  R              0,  Z 

It  is  at  once  apparent  that  these  two  cases  of  the 
law  of  pulsation,  occurring  in  different  circumstances, 
entirely  agree.  The  sequence  of  the  phenomena  which 
occur  at  the  death  of  the  nerve  on  the  application  of  cur- 
rents of  little  power  is  exactly  the  same  as  that  which 
may  be  elicited  from  a  fresh  nerve  by  gradually  increas- 
ing the  strength  of  the  current.  In  other  words,  if  the 
nerve  is  irritated  with  weak,  unvaried  currents,  these 
act  on  a  fresh  nerve,  after  a  time,  in  exactly  the  same 
way  as  currents  of  medium  strength,  and,  after  a 
somewhat  longer  time,  as  powerful  currents  would  have 
acted.  In  order  to  understand  this,  it  is  necessary  to 
recall  our  previous  experiences  of  the  changes  in  the 
excitability  at  the  death  of  the  nerve.  We  found  that 
in  that  case  the  excitability  at  first  rises  and  attains  a 
maximum  before  it  again  falls.  Supposing,  therefore, 
a  fresh  nerve  is  irritated  by  means  of  currents  of  definite 
but  weak  strength,  and  supposing  that  this  nerve  is  ex- 
amined after  the  lapse  of  a  short  time,  during  which  its 
excitability  has  risen,  it  is  evident  that  these  weak  cur- 


LAW    OF    PULSATIONS.  137 

rents  must  already  act  as  would  stronger,  and  that,  when 
the  excitability  has  risen  yet  further,  that  they  will  act  as 
very  strong  currents.  The  expressions  weak,  strong,  and 
medium  currents  bear  no  absolute  meaning,  the  same 
in  the  case  of  all  nerves,  but  must  always  be  under- 
stood relatively  to  the  excitability  of  the  nerve.  That 
which  in  the  case  of  one  nerve  is  a  weak  current  may 
evidently  act  as  much  stronger  in  the  case  of  another 
nerve  the  excitability  of  which  is  much  greater ;  and, 
moreover,  one  single  nerve,  at  different  times,  may  be 
conditioned  in  this  respect  as  though  it  were  two  diffe- 
rent nerves,  if  its  excitability  has  in  the  interval  under- 
gone considerable  changes.  There  can,  therefore,  be 
no  difficulty  in  understanding  how,  as  the  excitability 
gradually  rises,  the  action  of  weak  currents  gradually 
becomes  equal  to  that  of  medium  and  strong  currents. 
One  striking  fact  must,  hoAvever,  be  observed.  As  the 
excitability  after  it  has  reached  its  highest  point  begins 
to  fall  again  before  it  entirely  disappears,  it  might  be 
supposed  that  the  same  currents  which  at  the  extreme 
height  of  the  excitability  acted  as  strong  currents, 
would  now  act  again  as  currents  of  medium  strength, 
and  then  as  weak  currents,  before  they  entirely  lose 
their  power.  According  to  this,  the  third  stage  of 
excitability,  in  which  a  closing  pulsation  is  observable 
in  the  case  of  the  descending  current,  an  opening  pul- 
sation in  the  case  of  the  ascending  current,  should 
be  succeeded  by  a  fourth  and  a  fifth  stage,  of  which 
the  fourth  should  resemble  the  second,  and  the  fifth 
the  first.  This  has  indeed  been  said  to  occur  by  some 
observers,  but  it  does  not  appear  as  a  rule.  In  explana- 
tion of  this,  it  has  been  assumed  that  no  real,  but  only 
an  apparent  decrease  of  the  excitability  takes  place  after 


138     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

it  has  reached  its  highest  point.  It  must,  moreover,  be 
remembered  that  it  is  never  merely  a  single  cross-section 
of  a  nerve  which  is  irritated,  but  always  a  portion  of 
greater  extent,  and  that  the  excitability  measured  by  us 
is  in  reality  only  the  average  excitability  of  the  various 
points  within  the  irritated  portion.  It  may  further  be 
assumed  that  the  excitability  at  each  point,  when  it 
has  reached  its  height,  is  very  rapidly,  if  not  instan- 
taneously, destroyed.  As  this,  however,  occurs  sooner 
at  the  higher  than  at  the  lower  points,  it  follows 
also  that  the  excited  portion,  beginning  from  the  top, 
gradually  becomes  a  powerless  thread,  which  is,  how- 
ever, still  capable  of  transmitting  electricity.  The  ex- 
citement occurs  in  reality  only  in  the  lower  division  of 
the  portion  irritated,  and  this,  as  long  as  it  retains  any 
power  of  action,  must  remain  at  the  highest  point  of 
excitability.^ 

4.  In  studying  the  law  of  pulsations  we  attended 
only  to  the  closing  and  opening  of  the  current,  entirely 
disregarding  the  period  during  which  the  continuous 
current  flowed  through  the  nerve.  In  reality,  the 
nerve,  as  a  rule,  remains  unexcited  during  this  period. 
Sometimes,  however,  especially  on  the  application  of 
but  moderately  powerful  currents,  an  enduring  excite- 
ment expressing  itself  as  a  tetanus  in  the  muscle  is 
observable  while  the  current  lasts.  Ascending  and 
descending  currents  do  not  behave  quite  alike  in  this 
matter.  The  latter  are  followed  by  tetanus,  even  in  the 
case  of  currents  of  somewhat  high  power,  while  the 
ascending  currents  are  only  followed  by  tetanus  when 
they  are  weak.  In  all  cases  this  tetanus  is,  however, 
but  slight,  and  cannot  be  compared  with  that  which 
'  See  No'.es  and  Additions,  No.  5. 


RELATION    OF   ELECTROTON'US  TO    EXCITEMENT.       139 

may  be  induced  by  repeated  separate  irritations,  for 
instance,  by  inductive  shocks,  or  by  jErequently  and 
repeatedly  closing  and  opening  a  current.  It  thus 
appears  that  variable  currents  are  better  adapted 
for  effecting  the  excitement  of  a  nerve  than  are  con- 
stant currents.  Inductive  currents,  though  their  dm-a- 
tion  is  extremely  short,  may  be  regarded  as  similar  to 
constant  currents  which  are  re-opened  immediately 
after  being  closed.  True  pulsations  may  indeed  be  un- 
failingly elicited,  even  with  constant  currents,  if,  by 
using  suitable  apparatus,  they  are  but  momentarily 
closed,  and  are  then  again  reopened.  But  experience 
of  the  law  of  pulsations  shoAvs  that  either  the  closing 
or  the  opening  are  under  certain  circumstances  alone 
sufficient  to  elicit  pulsations.  As  we  know  that  the 
altered  condition  called  electrotonus  is  produced  in  the 
nerve  by  closing  the  current,  and  that  on  the  opening 
of  the  current  this  condition  gives  place,  if  not  im- 
mediately, yet  after  a  short  time,  to  the  natural  con- 
dition, we  may,  therefore,  assume  that  the  excitement 
of  the  nerve  is  actually  due  to  the  fact  that  the  nerve 
passes  from  a  natural  into  an  electrotonic  condition,  or 
back  again  from  this  into  its  natural  state.  We  may 
suppose  that  the  smallest  particles  of  the  nerve  are 
transferred,  on  the  intervention  of  electrotonus,  from 
their  normal  into  changed  positions,  and  that  this  mo- 
tion of  the  particles  is  under  certain  circumstances  con- 
nected with  excitement.  We  have,  however,  found 
that  a  nerve,  when  electrotonus  intervenes,  is  distin- 
guishable into  two  parts,  the  conditions  of  which  evi- 
dently differ ;  for  in  the  one,  that  of  kat electrotonus, 
the  excitement  is  increased,  while  in  the  other,  that 
of  anelectrotonus,  it  is  decreased.     It  might,  therefore, 


140 


PHYSIOLOGY    OF    MUSCLES   AND    NERVES. 


be  possible  that  these  two  conditions  differ  in  the  re- 
lation which  they  bear  to  the  excitement.  Indeed, 
Pfliiger  supposed  that  excitement  occurs  only  at  the 
commencement  of  katelectrotonus  and  at  the  cessation 
of  anelectrotonus.  On  the  basis  of  this  hypothesis  the 
phenomena  of  the  law  of  pulsations  may  be  explained ; 
and  it  becomes  intelligible  why  on  the  closing  and 
opening  of  the  current  pulsations  sometimes  occur  and 
are   sometimes  absent.      In  order,  however,  fully  to 


Fig.  33.    Electrotonus. 

understand  this  hypothesis  and  the  law  of  pulsations 
based  upon  it,  we  must  study  the  phenomena  of  elec- 
trotonus  more  closely  than  we  have  yet  done. 

5.  We  have  already  seen  that  the  excitability  is  in- 
creased on  the  side  of  the  kathode  during  the  closing 
of  the  current,  and  is  decreased  on  the  side  of  the 
anode.  Easy  as  it  is  to  prove  this  law  under  the  appli- 
cation of  weak,  or  medium  currents,  it  is  sometimes 
very  hard  to  do  so  when  the  current  causing  the  elec- 
trotonus   is  strong.      Let  us   again    imagine  that  the 


TRANSmSSION  OF  EXCITEMENT  DUKING  ELECTROTOXUS.  141 

nerve,  n  n'  (fig.  33)  is  traversed  between  c  and  d  by  an 
ascending  current,  and  that  it  is  irritated  between  the 
points  e  and/,  above  the  portion  traversed  by  the  current. 
The  muscle  is  accordingly  at  n\  as  in  our  previous  ob- 
servations. Irritation  takes  place  on  the  side  of  the 
kathode.  An  increase  in  the  excitability  should  there- 
fore occur.  This  may  easily  be  shown  when  the  cur- 
rents used  for  effecting  electrotonus  are  weak.  If, 
however,  the  current  used  for  this  purpose  is  somewhat 
strengthened,  no  increase  in  the  excitability  is  ob- 
servable ;  and,  indeed,  if  the  ciurrents  are  sufficiently 
strong,  it  becomes  quite  impossible  to  effect  contrac- 
tion in  the  muscle  by  irritation  at  ef.  This  may  seem 
to  afford  an  exception  to  the  law  of  the  electrotonic 
changes  in  the  excitability.  But  from  the  previous 
experiments  it  is  evident  that  this  must  not  be  in- 
ferred. Possibly  the  excitability  is  in  reality  increased 
at  e  /  in  entire  accordance  with  the  law ;  but  in  order 
that  the  action  of  the  excitement  at  this  point  should 
become  visible,  the  excitement  must  pass  through  the 
portion  under  the  influence  of  electrotonus,  as  well 
as  through  the  an  electrotonic  portion  lying  below  the 
latter,  and  it  may  be  supposed  that  this  propagation  of 
the  excitement  meets  with  an  insuperable  obstacle  in 
the  condition  of  strong  anelectrotonus  which  prevails 
there.  It  can  indeed  be  shown  that  this  is  the  case. 
If  the  current  is  reversed,  so  that  it  flows  in  a  descend- 
ing direction  through  the  nerve,  then  irritation  at 
the  portion  a  b  will  invariably  show  the  existence  of 
heightened  excitement,  however  strong  the  current 
may  be.  But  the  portion  a.  &  is  now  under  exactly  the 
same  conditions  as  was  the  portion  e/  previously.  It  is 
in  itself  very  improbable  that  the  nerve  acts  differently 


142  PHYSIOLOGY   OF   MUSCLES   AJ^D  IS^EEYES. 

in  two  sucli  entirely  similar  cases.  The  difference 
between  the  two  cases  consists  solely  in  the  fact  that 
in  the  latter  the  kateiectrotonic  point  examined  is 
situated  immediately  nest  to  the  muscle,  so  that  its 
condition  of  excitability  can  be  indicated  directly  by 
the  ninscle ;  while  in  the  case  first  observed,  the  con- 
dition of  excitability  at  the  point  e  f,  before  it  can  find 
expression  in  the  muscle,  must  find  means  of  passing 
througli  the  otherwise  altered  portions  c  d  and  a  h.  Now 
it  may,  on  the  other  hand,  be  shown  that  transmission 
in  a  nerve  under  the  influence  of  electrotonus  really 
takes  place  at  an  altered  speed.  In  the  kateiectrotonic 
portion  the  rate  of  propagation  is  but  little  altered — 
is,  perhaps,  slightly  increased;  but  in  the  anelectro- 
tonic  portion  it  is  markedly  decreased.  From  this  it 
may  be  inferred  that  anelectrotonus  not  only  decreases 
the  excitability,  but  also  hinders  the  propagation  of  the 
excitement;  and  that  where  the  anelectrotonus  is  strong, 
propagation  is  even  entirely  prevented. 

6.  This  not  only  exj)lains  the  apparent  exception  to 
the  laws  of  electrotonus,  but  also  affords  explanation  of 
the  feet  that  strong  ascending  currents,  when  closed, 
are  followed  by  no  pulsations.  "VTe  know  that  a  strong 
electric  current  induces  katelectrotonus  in  the  upper 
half,  anelectrotonus  in  the  lower.  According  to  Pfliiger's 
hvpothesis,  excitement  occurs  in  the  nerve  only  at  the 
point  at  which  katelectrotonus  intervenes;  that  is,  on 
the  closing  of  the  ascending  current,  in  the  upper  por- 
tion of  the  nerve.  In  order  to  reach  the  muscle,  this 
excitement  must  pass  through  the  lower  portion  of  the 
nerve,  and  as  this  is  strongly  anelectrotonic,  it  presents 
an  obstacle  to  the  further  passage  of  the  excitement. 
The  excitement  which  occurs  in  the  upper  half  is,  there- 


EXPLAXATIOX   OF   THE   LAW    OF   PULSATIONS.        143 

fore,  unable  to  reacli  the  muscle,  so  that  pulsation  is 
necessarily  absent  on  the  closing  of  the  current. 

In  order  to  apply  the  corresponding  case  to  the 
opening  of  a  descending  current,  the  help  of  another 
hypothesis  is  required,  according  to  which  the  great 
modification  which  follows  the  disappearance  of  katelec- 
trotonus,  and  which  so  greatly  decreases  the  excitability, 
also  involves  a  hindrance  to  transmission.  This  assump- 
tion has  not  yet  been  experimentally  proved ;  proof  is 
indeed  difficult,  on  account  of  the  ephemeral  charac- 
ter of  the  modifications.  The  similarity  of  necrative 
modification  to  anelectrotonus,  both  decreasing  the 
excitability,  favours  the  hypothesis  that  in  negative 
modification  also  an  obstacle  is  afibrded  to  transmission. 
According  to  this  view,  the  case  is  the  same  on  the 
opening  of  a  descending  current  as  on  the  closing  of  an 
ascending  current.  According  to  Pfliiger's  hypothesis 
excitement  occurs  on  the  opening  of  a  current  only  in 
that  portion  of  the  ner\  e  at  which  anelectrotonus  dis- 
appears. This,  in  the  case  of  a  descending  current, 
is  the  upper  portion  of  the  nerve.  In  order  to  reach 
the  muscle  thence,  the  excitement  would  have  to  tra- 
verse the  lower  portion,  which  is  at  the  same  time  taken 
possession  of  by  a  strong  negative  modification,  and  this 
prevents  propagation  of  the  excitement ;  no  opening 
pulsations,  therefore,  occmr  in  the  case  of  the  descend- 
ing current. 

Pfliigiir  supported  his  hypothesis  by  the  following 
experiment.  Mention  has  already  been  made  of  the 
so-called  Ritter's  tetanus,  which  intervenes  when  a 
current  which  has  traversed  a  nerve  for  some  time  is 
interrupted.  According  to  Pfliiger's  hypothesis,  this 
excitement  should  also  be  located  on  the  side  of  the 


144  THYSIOLOGY    OF   MUSCLES   AND    NERVES. 

anode.  If  an  ascending  current  is  passed  through  a 
nerve,  the  anode  side  is  situated  in  its  lower  portion ; 
but  if  the  current  is  descending,  then  it  is  situated  in 
the  upper  portion.  If  Eitter's  tetanus  is  induced  by 
means  of  a  descending  current,  and  if  the  nerve  is  bi- 
sected between  the  electrodes  immediately  after  the 
opening  of  the  current,  the  tetanus  at  once  ceases.  If 
the  same  experiment  is  ti-ied  with  an  ascending  current, 
then  the  cutting  of  the  nerve  in  no  way  influences  the 
tetanus. 

Yet  another  proof  of  the  truth  of  this  hypothesis  is 
afforded  by  Pflager's  study  of  the  excitement  of  the 
sensory  nerves  by  an  electric  current.  As  the  terminal 
apparatus  of  sensory  nerves,  by  the  action  of  which  the 
irritation  is  recognised,  is  situated  at  the  opposite  end 
of  the  nerve,  it  seems  that  the  law  of  pulsations  should 
prevail  in  an  opposite  way  to  that  in  which  it  pre- 
vails in  the  case  of  the  motor  nerves.  Pfliiger  as- 
certained that  in  reality  strong  ascending  currents 
induce  sensation  only  when  closed,  strong  descending 
currents  only  when  opened.  The  explanation  is  the 
same  in  this  case  as  in  that  of  the  motor  nerves.  On 
the  closing  of  the  descending  current,  excitement  oc- 
curs in  the  lower  portion  of  the  nerve.  In  order  to 
effect  sensation  the  excitement  must  pass  to  the  spinal 
marrow  and  the  brain ;  it  would  have,  therefore,  to  pass 
through  the  upper  parts  of  the  nerve,  where  it  would  be 
checked  by  the  strong  anelectrotonus  which  prevails 
there.  The  opening  of  the  ascending  current  has  a 
similar  irritating  effect  on  the  lower  parts  of  the  nerve. 
In  order  to  reach  the  spinal  marrow  and  brain,  this 
excitement  would  have  to  pass  through  the  upper  parts, 
where,  in  this  case,  it  would  be  checked  by  the  strong 
negative  modification. 


GENEEAL   LAW    OF  KEKVE   EXCITEMENT.  145 

The  only  explanation  of  the  fact  that  weak  currents, 
whatever  their  direction,  act  only  on  being  closed,  is 
that  the  changes  in  the  nerve  probably  begin  more 
quickly  than  they  disappear  on  the  closing  of  the  cur- 
rent. The  differences  are,  however,  very  slight;  and 
a  very  slight  strengthening  of  the  current  suffices  to 
elicit  opening  pulsations  of  the  nerve  also.  This  is 
especially  true-  of  the  descending  current ;  if  the  nerve 
is  not  quite  fresh,  opening  pulsations  may  occasionally 
be  observed  even  in  the  case  of  very  weak  currents 
which  do  not  as  yet  afford  any  closing  pulsations. 
This  is  connected  with  the  circumstance  that  the  ex- 
citability is  somewhat  greater  in  the  upper  than  in  the 
lower  portions  of  the  nerve.  The  natural  superiority 
of  the  closing  pulsation  is  thus  cancelled  in  the  case  of 
the  descending  current,  and  opening  pulsation  is  con- 
sequently rendered  more  easy. 

7.  From  what  has  been  said  it  seems  very  probable 
that  every  excitement  in  the  nerve  is  due  to  a  change 
in  its  condition,  which  might  be  directly  shown  in  the 
case  of  the  electric  current  by  the  electrotonic  change 
in  the  excitability.  The  more  quickly  these  changes 
occur,  the  more  easily  are  they  able  to  excite  the 
nerve.  This  law  is  exhibited  even  in  the  case  of 
non-electric  excitement.  It  is,  for  instance,  possible 
by  gradually  increasing  pressui'e  on  the  nerve  entirely 
to  crush  the  latter  without  producing  any  excitement, 
though  every  sudden  pressure  is,  as  we  have  seen, 
inseparable  from  excitement.  A  similar  fact  may  be 
observed  in  the  case  of  thermic  and  chemical  irrita- 
tion. From  this  it  may  be  inferred  that  the  excitement 
in  the  nerve  is  due  to  a  certain  form  of  motion  of  its 
smallest  particles,  and  that  a  sudden  blow  is  better 


146     PHYSIOLOGY  or  MUSCLES  AND  NERVES. 

adapted  for  exciting  this  motion  than  is  slow  action. 
That  even  slight  mechanical  disturbances  are  capable 
of  producing  excitement,  although  the  nerve  is  not 
crushed,  has  been  proved  by  Heidenhain.  He  attached 
a  small  ivory  hammer  to  the  instrument  which  we  have 
already  described  under  the  name  of  Wagner's  hammer, 
and,  having  laid  the  nerve  on  a  small  ivory  anvil, 
placed  the  latter  under  the  hammer  in  such  a  way 
that  the  latter  tapped  gently  on  the  nerve.  The  result 
of  this  was  strong  tetanus  lasting  for  several  seconds. 
To  obtain  a  more  accia-ate  conception  of  the  mechanism 
of  nervous  excitement,  it  would  be  necessary  first  to 
learn  accurately  the  arrangement  of  the  smallest  par- 
ticles in  the  quiescent  nerve.  Now  we  shall  later  on 
examine  certain  behaviour  of  the  quiescent  nerve  from 
which  conclusions  may  be  drawn  as  to  the  regular 
arrangement  of  the  smallest  particles.  While  postpon- 
ing the  closer  examination  of  these  details,  we  may  at 
present  try  to  explain  the  facts  of  excitement  as  clearly 
as  circumstances  permit.  For  this  end  we  will  assume 
that  the  particles  of  the  nerve  are  retained  in  an  en- 
tirely definite  relative  position  by  molecular  forces. 
Excitement  can,  accordingly,  only  intervene  when  the 
particles  are  displaced  from  this  position  and  are  set  in 
motion.  The  more  powerful  are  the  forces  which  retain 
the  particles  in  their  balanced  position,  the  greater 
must  be  the  forces  which  move  them,  and,  therefore, 
the  smaller  is  the  excitability.  It  must  also  be  ex- 
plained that  the  separate  particles  of  the  nerve  mutu- 
ally influence  each  other,  each  particle  influencing  the 
ol  her  and  helping  to  retain  it  in  its  relative  position. 
A  comparison  drawn  by  du  Bois-Reymond  may  be  used 
to    make   this    somewhat   involved    explanation  more 


GENERAL    LAW    OF   NERVE    EXCITEMENT.  147 

intelligible.  It  is  a  well-known  fact  tliat  a  magnetic 
needle  suspended  by  a  thread  assumes  such  a  position, 
in  consequence  of  the  magnetic  attraction  of  the  earth, 
that  one  of  its  ends  points  to  the  north,  the  other  to 
the  south.  Now,  su2Dj)osing  a  series  of  many  magnetic 
needles,  all  suspended  one  behind  the  other  in  the  same 
meridian  line,  as  in  fig.  34,  then  each  of  these  needles 

NS  NS  NS  NS  NS 

~J~        ~Y~         ^         "T"         ~5~ 

Fig.  3L    A  siiuiES  of  siagnktic  nkedles  arranged  as  a  diagram 

OF  THE   PAUTICLES  OF   A   NERVE. 

will  be  yet  more  firmly  retained  in  its  position  by  its 
neighbours,  for  the  adjacent  north  and  south  poles  of 
the  needles  mutually  attract  each  other.  If,  for  ex- 
ample, we  wish  to  move  the  middle  needle.  No.  3,  more 
force  must  be  used  to  do  this  than  would  be  necessary 
if  the  needle  were  alone.  But  when  the  centre  needle 
is  turned,  the  immediately  adjacent  needles  cannot  re- 
main at  rest,  but  are  similarly  deflected ;  these  exercise 
a  similar  deviating  influence  on  their  neighbours ;  and 
so  on.  So  that  the  disturbance  created  at  one  point 
in  this  series  of  magnetic  needles  passes  like  a  wave 
through  the  whole  series. 

This  evidently  bears  much  resemblance  to  that 
which  takes  place  in  nerves.  It  explains  not  only 
how  a  disturbance  commencing  at  any  point  in  the 
nerve  propagates  itself,  but  also  how  each  separate  part 
of  the  nerve  is  able  to  influence  the  other  parts.  We 
have  already  found  that  the  excitability  of  any  point  of 
the  nerve  increases  if  the  immediately  superior  portion 
of  the  nerve  is  cut  away.  The  magnetic  needles  show 
that  just  in  the  same  way  each  is  more  readily  move- 


148  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

able  when  some  of  its  neighbours  have  been  removed. 
Without,  therefore,  assuming  other  resemblances  be- 
tween the  forces  which  act  on  the  magnetic  needles 
and  those  present  in  the  nerve,  we  may  accept  the 
comparison  so  far  that  we  may  imagine  the  nerve  to 
consist  of  separate  minute  particles,  arranged  one  behind 
the  other  in  the  longitudinal  direction  of  the  nerve, 
and  mutually  retaining  each  other  in  their  position. 
Now,  if  there  are  forces  which  retain  the  particles  in 
this  relative  position  yet  more  firmly,  it  is  evident  that 
they  must  lessen  the  excitability ;  while,  on  the  other 
hand,  such  forces  as  tend  to  move  the  nerve-particles 
from  their  relative  positions  must  at  the  same  time 
decrease  the  strength  of  their  connection,  and  must 
therefore  render  the  nerve  more  excitable.  As  regards 
the  electric  current,  we  have  seen  that  the  two  poles 
act  on  the  nerve  in  opposite  ways.  We  may,  therefore, 
assume  that  by  one  pole,  the  positive,  the  nerve  par- 
ticles are  retained  in  their  quiescent  position,  while  by 
the  negative  pole,  on  the  other  hand,  they  are  disturbed 
from  this  position.  If  this  is  the  case,  it  explains  the 
fact  that  excitement  occurs  only  at  the  negative  pole 
when  the  current  is  closed.  The  excitability  is  in- 
creased at  the  positive  pole  on  the  opening  of  the  cur- 
rent; here,  therefore,  there  occurs  a  movement  of  the 
particles  such  as  follows  the  closing  in  the  negative 
pole,  so  that  in  this  case  the  excitement  can  occur  on 
the  opening  of  the  current. 

The  fact  that  the  nerve  remains  unexcited  by 
changes  in  its  condition,  although  these  same  changes 
if  they  occur  suddenly  do  induce  excitements,  bears  so 
sio-nificantly  on  the  explanation  of  the  nervous  processes, 
that  we  must  study  it  in  yet  greater  detail.     The  fact 


GENERAL  LAW  OF  NERVE  EXCITEMENT. 


149 


may  be  most  easily  and  surely  sliown  in  the  case  of 
electric  excitement,  as  there  is  no  difficulty  in  allowing 
the  strength  of  the  currents  to  increase  or  decrease 
more  or  less  gradually.  Let  the  apparatus  be  arranged 
as  in  fig.  35    in  which   the   nerve   is  traversed  bv  a 


Fig.  35.     Riieochoud. 

current,  the  strength  of  which  may  be  altered  by  moving 
the  slide  S.  Let  a  key  be  inserted  in  the  circle,  and  let 
the  slide  be  so  placed  that  pulsations  occur  on  the 
closing  and  the  opening  of  the  current.  On  placing  the 
slide  S  close  to  A  (in  which  position  the  resistance  in 
the  branch  J.  ^  is  nil,  so  that  no  current  passes  through 
the  nerve),  and  pushing  it  slowly  forward  to  its  former 
position  at  S,  the  current  within  the  nerve  slowly  in- 
creases from  zero  to  its  former  strength  :  on  again  push- 
ing the  slide  slowly  back  till  it  touches  A,  the  strength 
of  the  current  again  slowly  decreases  to  0.  In  neither 
of  these  cases  is  the  nerve  excited.  As  soon,  however, 
as  the  movement  of  the  slide  is  in  any  way  effected 

*  E.  du  Bois-Eeymond  has  described  apparatus  of  this  sort  ur.der 
the  name  of  ScJt?i'ankit»ff,vJteocJiord. 


150  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

with  great  speed,'  the  nerve  is  ezcited  and  the  muscle 
pulsates.  When,  therefore,  the  current  being  closed 
or  opened  by  means  of  the  key,  the  nerve  is  excited, 
this  is  due  to  the  fact  that  the  strength  of  the  current 
increases  with  great  rapidity  from  zero  to  its  full 
strength,  or  sinks  from  the  latter  to  zero. 

The  facts  thus  observed  explain  why  inductive 
shocks,  which  are  of  but  very  short  duration,  and  in 
which  closing  and  opening  follow  each  other  in  such 
rapid  succession,  are  so  especially  capable  of  exciting 
the  nerve.  All  inductive  shocks  are  not,  however, 
equally  adapted  for  this  purpose.  When,  making  use 
of  the  inductive  apparatus  already  described,  the  current 
in  the  primary  coil  is  closed  and  then  interrupted,  the 
result  is  the  creation  of  two  currents  differing  in  their 
direction  in  the  secondary  coil,  these  being  the  closing 
inductive  current  and  the  opening  inductive  current. 
If  these  are  made  to  pass  through  a  nerve,  the  exciting 
influence  of  the  latter  is  alwa;ys  much  greater  than  that 
of  the  former.  This  can  be  very  plainly  shown  by 
placing  the  secondary  coil  at  a  distance  from  the  pri- 
mary. By  this  means,  a  distance  may  always  be  found 
at  which  the  opening  inductive  current  is  active,  while 
the  closing  inductive  current  as  yet  exercises  no  in- 
fluence ;  if  the  coils  are  then  brought  nearer  to  each 
other,  the  latter  also  becomes  active.  If,  however, 
when  the  coils  of  the  inductive  apparatus  are  in  any 
position,  the  secondary  coil  is  connected  with  a  multi- 
plier, then  the  deflections  of  the  magnetic  needle  are 
always  of  equal  strength  in  the  case  of  both  inductive 
currents.  The  nerve,  therefore,  exhibits  a  difference 
which  the  multiplier  is  incapable  of  indicating.  It  has, 
however,  been  shown  that  the  two  inductive  currents 


GENERAL  LAW  OF  NERVE  EXCITEMENT.      151 

differ  entirely  in  duration.  The  closing  inductive  cur- 
rent increases  slowly,  and  decreases  just  as  slowly, 
while,  on  the  other  hand,  the  opening  inductive  current 
very  rapidly  attains  its  full  strength  and  ends  just  as 
quickly.  It  is  to  this  difference  that  the  latter  evi- 
dently owes  its  greater  j)hysiological  effect.^ 

Let  us  return  to  the  experiment  as  first  arranged 
with  the  rheochord.  Instead  of  pushing  ah>ng  the 
slide  between  A  and  *S^^  it  may  be  moved  backward  or 
forward  between  any  two  points.  The  current  in  the 
nerve,  in  this  case,  never  ceases,  but  is  either  strength- 
ened or  weakened  according  to  the  direction  in  which 
the  slide  is  moved.  If  the  latter  is  moved  suddenly 
and  with  great  speed,  it  may  produce  excitement ;  but 
the  nerve  always  remains  unexcited  when  the  move- 
ment is-  gradual.  It  therefore  appears  that  it  is  not 
the  actual  closing  and  opening  of  a  current  which  is 
required  to  excite  the  nerve,  but  that  any  change, 
whether  it  strengthens  or  weakens  the  current,  is  suffi- 
cient to  effect  this,  provided  that  the  alteration  is 
sufficiently  great  and  sufficiently  rapid.  Closing  and 
opening  are  but  special  cases  of  alteration  of  the  cur- 
rent in  which  one  of  the  limits  to  the  strength  of  the 
current  =  0.  The  following  law  regarding  the  electric 
excitement  of  nerve  may  therefore  be  stated:  any 
change  in  a  current  traversing  a  nerve  may  excite  the 
latter  if  it  is  sufficiently  strong^  and  if  it  occurs  luith 
sufficient  speed.  We  have  however  seen  that  this  law 
has  very  many  exceptions.  For  under  certain  circum- 
stances a  greater  alteration  (the  closing  of  a  strong 
ascending  current)  may  appear  to  be  without  effect,  al- 
though one  less  strong  takes  effect.  If,  however,  it  is 
'  See  Notes  aud  Additions,  Xo  6. 


152  FHYSIOLOGY    OF    MUSCLES    AND   NERVES._ 

admitted  that  in  such,  cases  excitement  does  in  reality 
take  place,  but  that  it  is  not  observable  on  account  of 
external  circumstances  (hindrance  to  the  propagation  tp 
the  muscle),  then  these  exceptions  may  be  said  to  be 
merely  apparent.  Moreover,  assuming  that  the  changes 
in  the  strength  of  the  currents  within  the  nerve  only 
excite  in  consequence  of  the  fact  that  they  bring  about 
changes  in  the  molecular  condition  of  the  nerve,  and 
combining  with  this  all  that  we  know  of  the  effect  of 
other  forms  of  nerve  irritation,  the  following  law  regard- 
ing nervous  excitement  may  be  regarded  as  the  final 
result : — 

Excitement  of  the  nerve  depends  on  a  change  in 
its  molecular  condition.  It  occurs  as  soon  as  such  a 
change  is  effected  with  sufficient  speed. 

It  may  be  added  that  this  law  is  in  all  essential 
points  true  also  of  muscle.  But  it  appears  that  the 
molecules  of  muscle  are  more  sluggish  than  are  those 
of  nerve,  so  that  in  the  former  very  transient  influences 
may  more  easily  be  without  effect.^ 

'  See  Notes  and  Additions,  Nos.  7  and  8. 


CHAPTEE   IX. 

i.  Electric  phenomena;  2.  Electric  fishes;  3.  Electric  organs; 
1.  Multiplier  and  tangent  galvanometer ;  5.  Difficulty  of  the 
study;  6.  Homogeneous  diverting  vessels ;  7.  Electromotive 
force  ;    8.  Electric  fall ;    9.  Tension  in  the  closing  arch. 

1.  As  yet  in  examining  the  essential  qualities  of 
muscles  and  nerves  we  have  disregarded  a  series  of 
important  phenomena  common  to  both,  in  order  that 
we  may  now  treat  them  as  a  whole.  We  refer  to  the 
electric  actions  which  proceed  from  these  tissues. 
Muscles  and  nerves  are  especially  distinguished  among 
all  other  tissues  of  the  animal  body  by  the  fact  that 
they  exercise  very  regular  and  comparatively  powerful 
electric  action ;  and  from  the  relation  existing  between 
electric  currents  and  the  excitability  of  muscles  and 
nerves  it  may  be  inferred  that  these  independent  elec- 
tric actions  bear  some  relation  to  the  essential  qualities 
of  muscles  and  nerves. 

It  is  true  that  electric  action  is  exhibited  in  other 
animal,  as  well  as  vegetable  tissues ;  but  these  are  very 
slight,  and  are  apparently  insignificant.'  Electric  cur- 
rents are  so  easily  generated  under  all  circumstances 
that  it  is  not  very  surprising  that  traces  of  them  are 

'  An  exception  is  perhaps  afforded  by  the  electric  phenomena 
of  the  leaves  of  Lioiuea  miturijwla  which  will  presently  be  men- 
tioned. 


154  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

everywhere  to  be  found.  In  the  researches  in  which 
we  are  aboiit  to  engage,  we  must  always  endeavour  as 
far  as  possible  to  exclude  these  accidental  currents,  or 
at  least  to  distinguish  them  froixi  those  currents  which 
it  is  our  task  to  examine,  and  the  causes  of  which  lie 
in  the  animal  tissues  themselves.  Apart  from  muscles 
and  nerves,  but  one  tissue  seems  endowed  with  some- 
what strong  electric  action  ;  this  is  that  of  the  glands. 
This  has,  indeed,  not  as  yet  been  fully  proved,  but  it 
has  been  shown  to  be  in  a  very  high  degree  probable. 
In  connection  with  this  it  is  a  very  interesting  fact  that 
the  glands  are  in  some  phj^siological  respects  very  similar 
to  the  muscles,  and  that  they  bear  the  same  relations 
to  nerves  as  do  muscles. 

2.  There  is,  on  the  other  hand,  a  tissue  in  which 
electric  action  is  exhibited  in  far  greater  strength,  so 
that  its  nature  was  known  long  before  it  was  recog- 
nised that  muscles  and  nerves  possess  the  same  capa- 
city. This  tissue  does  not,  however,  occur  in  all 
animals,  but  only  in  a  few  fishes,  which  on  this  account 
are  called  electric  fishes.  In  these  animals  special 
organs  of  peculiar  structure  occur,  in  which,  as  in  an 
electric  battery,  currents  of  \ery  considerable  strength 
arise,  the  discharge  of  which  is  caused  by  the  influence 
of  the  will,  the  animal  using  this  power  to  frighten  its 
enemies,  or  to  benumb  and  kill  its  prey.  Long  before 
the  world  knew  anything  accurately  as  to  the  physical 
nature  of  electric  phenomena,  such  powerful  influences 
as  are  exhibited  in  electric  fishes  did  not  fail  to  attract 
the  attention  of  chance  observers.  Notices  of  these 
remarkable  phenomena  are  actually  found  in  ancient 
writers ;   and  the   Koman   poet  Claudius    Claudianus ' 

'  He  lived  in  Alexandria  toward  the  end  of  the  fourth  century. 


ELECTRIC   FISHES.  155 

has  given  a  very  vivid  description  of  these  actions  in 
the  following  lines  : — 

'  Who  has  not  heard  of  the  power  of  the  dreadful 
ray,  of  the  benumbing  force  to  which  it  owes  its  name.^ 
Formed  only  of  gristle,  it  swims  slowly  against  the 
waves  or  creeps  sluggishly  on  the  waterwashed  sand. 
Nature  has  armed  it  with  an  icy  poison,  has  poured 
into  its  marrow  coldness  to  freeze  and  stiffen  all  living- 
things,  and  has  filled  it  with  everlasting  winter.  To 
these  gifts  of  nature  it  adds  craft,  and,  conscious  of 
power,  it  remains  quietly  stretched  among  the  sea- 
grasses  ;  yet  when  some  animal,  swimming  upward  to 
the  sea-top,  passes  near,  unpunished  it  fearlessly  feeds 
on  the  living  limbs.  Nor  when,  having  carelessly  bitten 
at  some  bait,  it  feels  the  line,  the  bent  hook  in  its  mouth, 
does  it  attempt  flight,  biting  itself  free,  but  craftily 
creeping  yet  nearer  to  the  dark  hair-line,  conscious  of 
its  power,  it  pours  the  electric  breath  from  its  poison- 
ous veins  far  and  wide  o^'er  the  water.  The  electric 
fluid  flashes  along  hook  and  line,  harming  even  the 
fisherman  where  he  stands  above  the  water ;  from  the 
lowest  depth  the  dreadful  lightning  flashes,  and  passing 
along  the  hanging  line,  by  the  magic  of  its  power 
carries  cold  as  of  ice  through  the  rod,  wounding  the 
strong  arm  and  curdling  the  blood  of  the  fishermen, 
who,  terror-struck,  throws  away  the  baneful  prey,  and, 
careless  of  his  line,  hurries  homeward  with  dismay.' 

After  the  theory  of  electricity  had  received  a  new 
development  in  consequence  of  the  discoveries  of 
Galvani  and  Volta,  these  fishes  were  frequently  studied 

Older  notices  of  tlie  Torpedo  occur  in  Plin}%  J^llian,  Opjiian  (wliosc 
poem  on  fishing  Claudianus  appears  to  have  known),  and  in  Aristotle. 
'  Torpedo,  from  ^yr/-'<w  =  numbness. 


156  PHYSIOLOGY    OF   MUSCLES   AJSD   NERVES. 

by  various  observers,  and  the  electric  character  of  their 
innate  force  was  incontrovertibly  shown.  Faraday's 
study  of  the  electric  eel,  and  du  Bois-Eeymond's  of 
another  electric  fish,  are  especially  important. 

There  are  three  fishes,  especially,  which  have  been 
proved  to  possess  this  capacity  for  giving  electric  shocks. 
These  are,  the  electric  ray  of  the  Adriatic  and  Medi- 
terranean (Torpedo  electrica  and  T.  niarmorata) ;  the 
electric  eel  (Gh/mnotus  electricus),  which  occurs  in  the 
fresh  waters  of  South  America ;  and  lastly,  another  elec- 
tric fish  (J\Ialajjteriirus  electricus  or  M.  beninensis), 
which  has  but  recently  been  carefully  studied,  and 
which  occurs  in  the  rivers  of  the  Bay  of  Benin  on  the 
east  coast  of  Africa.  We  cannot  omit  this  opportunity 
of  inserting  Alexander  A'on  Humboldt's  description  of 
the  electric  eel  and  its  action  ^ : — 

'  The  crocodile  and  the  jaguar  are  not,  however,  the 
only  enemies  that  threaten  the  South  American  horse ; 
for  even  among  the  fishes  it  has  a  dangerous  foe.  The 
marshy  waters  of  Bera  and  Eastro  are  filled  with  innu- 
merable electric  'eels,  which  at  pleasure  are  able  to 
discharge  a  deadening  shock  from  every  part  of  their 
slimy,  yellow-speckled  bodies.  This  species  of  gymnotus 
is  about  five  or  six  feet  in  length.  It  is  powerful  enough 
to  kill  the  largest  animals  when  it  discharges  its  ner- 
vous organs  at  one  shock  in  a  favourable  direction.  It 
was  once  found  necessary  to  change  the  line  of  road 
from  Uritucu  across  the  savannah  owing  to  the  number 
of  horses  which,  in  fording  a  certain  rivulet,  aimually 
fell  a  sacrifice  to  these  electric  eels,  which  had  accu- 
mulated there  in  great  numbers.  All  other  species  of 
fish  shun  the  vicinity  of  these  formidable  creatures. 
*   'fl,en;s  of  Nature. 


ELECTRIC   EELS.  157 

Even  the  angler,  when  fishing  from  the  high  bank,  is 
in  dread  lest  an  electric  shock  should  be  conveyed  to 
him  along  the  moistened  line.  Thus,  in  these  regions, 
the  electric  fire  breaks  forth  from  the  lowest  depths  of 
the  waters. 

'  The  mode  of  capturing  the  gymnotus  afifords  a  pic- 
turesque spectacle.  A  number  of  mules  and  horses  are 
driven  into  a  swamp,  which  is  closely  surrounded  by 
Indians,  until  the  unusual  noise  excites  the  daring  fish 
to  venture  on  an  attack.  Serpent-like,  they  are  seen 
ssvimming '  along  the  surface  of  the  water,  striving 
cunningly  to  glide  under  the  bellies  of  the  horses. 
By  the  force  of  their  invisible  blows  numbers  of  the 
poor  animals  are  suddenly  prostrated ;  others,  snorting 
and  panting,  their  manes  erect,  their  eyes  wildly  flash- 
ing with  terror,  rush  madly  from  the  raging  storm ; 
but  the  Indians,  armed  with  long  bamboo  poles,  drive 
them  back  into  the  midst  of  the  pool. 

'  By  degrees  the  fury  of  this  unequal  contest  begins 
to  slacken.  Like  clouds  that  have  discharged  their 
electricity,  the  wearied  eels  disperse.  They  require 
long  rest  and  nourishing  food  to  recover  the  galvanic 
force  which  .they  have  so  freely  expended.  Their 
thocks  become  weaker  and  weaker.  Terrified  by  the 
noise  of  the  trampling  horses,  they  timidly  approach 
the  brink  of  the  swamp,  where  they  are  wounded  by 
harpoons,  and  drawn  on  shore  by  non-conducting  poles 
of  dry  wood. 

'  Such  is  the  remarkable  contest  between  horses  and 
fish.  That  which  constitutes  the  invisible  but  living 
weapon  of  these  inhabitants  of  the  water — that  which, 
awakened  by  the  contact  of  moist  and  dissimilar  par- 
ticles, circulates  through  all  the  organs  of  animals  and 


158  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

plants — that  which,  flashing  amid  the  roar  of  thunder, 
illuminates  the  wide  canopy  of  heaven — which  binds 
iron  to  iron,  and  directs  the  silent  recurring  course  of 
the  magnetic  needle  all,  like  the  varied  hues  of  the 
refracted  ray  of  light,  flow  from  one  common  source, 
and  all  blend  together  into  one  eternal  all-pervading 
power.' 

3.  All  electric  fishes  are  distinguished  by  the  pos- 
session of  peculiar  organs  in  which  the  electric  discharge 
originates.  These  resemble  powerful  batteries,  which 
can  be  put  in  action  by  the  will  of  the  animal,  and 
which  then  generate  currents  which,  passing  through 
the  water,  meet  and  act  upon  other  animals  which 
happen  to  be  near,  so  that  the  latter  may  even  be 
thus  killed.  These  electric  organs,  as  they  are  called, 
are  formed  on  the  same  plan  in  all  the  three  above-men- 
tioned genera  of  fishes.  They  consist  of  a  large  number 
of  minute  and  delicate  plates  which,  arranged  side  by 
side  and  enclosed  in  coverings  of  connective  tissue, 
form  the  whole  organ.  In  the  Torpedo  these  organs 
lie  flat  on  either  side  of  the  vertebral  column.  In  the 
Gymnotus  and  the  Malapterarus  they  are  arranged 
longitudinally ;  and  in  the  latter  they  form  a  closed 
tube,  in  which  the  animal  is  concealed,  its  head  and 
tail,  as  it  were,  alone  projecting.  The  separate  plates 
of  which  the  organ  consists  are  arranged,  therefore, 
horizontally  in  the  Torpedo,  vertically  in  the  Gymnotus 
and  Malapterurus.  Each  of  these  plates  consists  of 
an  extremely  delicate  membrane  which,  when  the  organ 
is  in  a  state  of  activity,  exhibits  positive  electricity  on  the 
one  side,  negative  on  the  other.  The  currents  of  the 
numerous  plates  combine  as  in  a  battery,  and  thus  all 
together  afford  a  very  powerful  cinrrent.     With  each 


THE    MULTIPLIER. 


159 


plate  is  connected  a  nerve-fibre,  by  means  of  which 
the  animal  is  capable  of  voluntarily  effecting  the  elec- 
tric discharge,  just  as  voluntary  muscular  contractions 
can  be  effected  by  means  of  the  nerve.  These  nerves 
may  also  be  artificially  irritated,  with  the  result  of  pro- 
ducing one  or  more  electric  shocks,  just  as  irritation  of 
a  motor  nerve  elicits  one  or  more  muscular  contraction. 
The  analogy  of  electric  organs  and  of  muscle  is,  in  fact, 
from  a  physiological  point  of  view,  complete. 

Mention  must  yet  be  made  of  the  fact  that  forms 
nearly  allied  to  these  fishes — for  instance,  the  various 
forms  of  Mormyrus^  which  in  structure  resemble  rays — 
possess  similar  organs,  though  these  have  not  as  yet 
been  shown  with  any  certainty  to  be  capable  of  any 
electric  action.  It  has,  moreover,  been  assumed  that 
the  luminous  organs  of  certain  insects  are  to  be  referred 
to  electric  forces ;  but  this  has  not  been  in  any  way 
proved. 

4.  Before  entering  further  into  the  statement  of  the 
electric  phenomena  in  animal  structures  it  will  be  neces- 
sary to  say  something  of  electric  phenomena  in  general, 
and  of  the  means  of  exhibiting  them. 

It  is  well  known  that  an  electric  current  results 
when  two  different  metals  are  in  contact 
with  each  other,  or  with  a  fluid.  Elec- 
tricity occurs  in  this  case  as  a  current, 
that  is,  in  a  state  of  motion  ;  while  in 
other  c.vses  it  exists  in  a  quiescent  con- 
dition. On  immersing  a  piece  of  copper 
and  a  piece  of  zinc,  as  in  fig.  36,  in  a  glass 
containing  diluted  sulphuric  acid,  and  then 
uniting  these  above  the  fluid  by  a  wire, 
the  positive  electricity  passes  through  the  wire  from  the 


iMG.    36. 

\X     EI.KfTRIC 

CLKKKNT. 


160     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

copper  to  the  zinc,  and  through  the  liquid  from  the  zinc 
to  the  copper.  A  magnetic  needle  is  used  to  indicate 
the  presence  of  such  a  current.  An  electric  current,  if 
made  to  pass  parallel  to  a  magnetic  needle,  deflects 
the  latter  from  its  normal  position,  and  tends  to  place 
it  at  right  angles  to  its  original  position.  According 
to  the  direction  in  which  the  positive  electricity  flows, 
and  according  to  the  position  of  the  conducting  wire 
relatively  to  the  magnetic  needle,  the  north  pole  of 
the  needle  is  deflected  either  to  the  east  or  to  the  west ; 
so  that  not  only  the  actual  presence  of  an  electric  cur- 
rent may  be  shown  by  means  of  a  magnetic  needle,  but 
its  direction  in  the  wire  may  also  be  determined.  This 
simple  means,  however,  only  serves  the  piurpose  when 
the  current  is  comparatively  strong,  for  the  magnetic 
needle  is  retained  in  its  position  by  the  attraction  of 
the  earth,  and  the  magnetic  current  must  overcome 
this  before  it  can  deflect  the  needle.  In  order  to  detect 
weak  cm-rents,  the  wire  through  which  the  current  flows 
is  wound  in  several  coils  round  the  needle.  As  each 
coil  exercises  a  force  tending  to  cause  the  deflection 
of  the  needle,  the  deflecting  force  is  increased  ;  and  an 
instrument  of  this  sort  is,  therefore,  called  a  multiplier.^ 
In  order  to  increase  the  sensitiveness  of  this  still  further, 
the  attraction  of  the  earth  must  be  annihilated  as  far 
as  possible,  so  that  even  weak  currents  are  able  to  cause 
deflection.  This  is  accomplished,  for  instance,  by  ar- 
ranging a  fixed  magnet  above  or  below  the  magnetic 
needle,  so  that  it  acts  on  the  latter  in  a  direction  con- 

'  If  attention  is  paid  to  certain  circumstances,  which  cannot  be 
mentioned  in  detail  here,  the  same  instrument  can  also  be  used  to 
measure  the  strength  of  currents  j  it  is,  therefore,  also  called  a  gal- 
vanometer. 


THE   MULTIPLIER    OR    GALVANOMETER. 


161 


trary  to  that  of  the  attraction  of  the  earth,  and  by 
carefully  bringing  this  magnet  nearer  until  the  action 
of  the  earth  is  almost  entirely  cancelled.    Or  two  mag- 


EiG.  37.    A  MeLTirnKR. 


netic  needles,  as  similar  as  possible,  are  connected  by  a 
fixed  intermediate  piece  in  such  a  way  that  the  corre- 
sponding poles  are  turned  in  opposite  directions.  As 
the  force  of  trravitation  now  tends  to   turn   the    two 


162  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

needles  in  opposite  directions,  the  force  of  attraction 
of  the  earth-magnetism  is  entirely,  or  almost  entirely 
removed,  so  that  even  very  weak  electric  currents,  if 
caused  to  pass  round  the  needle  in  a  suitable  way,  can 
cause  a  noticeable  deflection  of  the  needle. 

Fig.  37  represents  a  sensitive  multiplier  of  a  form 
well  suited  for  physiological  experiments.  The  two 
needles  are  connected  together,  and  are  suspended  by 
means  of  a  thread  of  silk  from  the  frame  h'  h;  the  screw 
i  serves  to  raise  the  needles  to  a  proper  height,  so  that 
one  of  them  can  move  freely  within  the  coils  of  the  wire, 
the  other  above  the  latter  and  over  a  graduated  circle,  by 
which  the  deflection  effected  by  the  current  can  be  mea- 
sured. The  very  thin  wire,  enclosed  in  silk,  is  wound 
on  to  the  frame  G ;  the  binding  screws  /'  /  serve  to 
transmit  the  current. 

The  use  of  the  multiplier  for  physiological  purposes 
has  recently  considerably  decreased,  owing  to  the  more 
perfect  adaptation  of  another  form  of  apparatus,  called 
the  tangent  galvanometer,  for  such  purposes.  The  ad- 
vantage of  this  consists  in  the  fact  that  it  is  not  only 
very  sensitive,  but  it  also  allows  the  strength  of  the 
current  to  be  measured.  If,  for  example,  the  deflec- 
tions of  the  magnetic  needle  are  very  slight,  the  strength 
of  the  currents  may  be  regarded  as  proportionate  to  the 
trigonometrical  tangents  of  the  angle  of  deflection.'  In 
order  to  measure  slight  deflections  of  this  sort,  our 
former  method  of  observation  by  means  of  the  mirror 
and  lens  may  be  used  (chap,  iv.,  §  3,  p.  57).  Either 
the  magnet  is  in  itself  reflecting,  or  it  is  connected 
with  a  mirror,  and  is  suspended  by  a  silk  thread  in  a 
copper  sheath.  A,  which  is  closed  by  plates  of  looking- 
'  See  Notes  and  Additions,  No.  9. 


THE    REFLECTING    GALVANOMETER. 


163 


glass.  The  electric  current  can  be  transmitted  through 
the  coils  B'  B,  which  move  on  slides,  in  oi'der  that  by 
their  greater  or  lesser  distance  from  the  magnet,  the 


sensitiveness  of  the  instrument  may  be  graduated  at 
will.  In  order  to  measure  the  deflections,  a  graduated 
scale  is  placed  parallel  to  the  mirror  when  in  its  qui- 


164.  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

escent  position,  and  its  reflection  is  observed  through 
the  lens  as  described  in  Chap.  IV.,  §  3.  This  may  also 
be  used  to  render  the  deflection  visible  to  a  large  audi- 
ence, by  allowing  the  light  of  a  suflficiently  powerful 
lamp  to  fall  on  the  mirror  and  throwing  the  reflection 
on  to  a  screen  by  means  of  a  lens.  In  order  to  in- 
crease the  sensitiveness  of  the  instrument,  the  influence 
of  gravitation  on  the  deflecting  magnet  is  decreased,  as 
already  described,  by  means  of  a  properly  arranged 
magnet. 

5.  Having,  in  one  or  other  of  these  ways,  provided 
as  sensitive  a  multiplier  as  may  be,  all  that  is  necessary 
is  to  connect  the  animal  substances  which  are  to  be  ex- 
amined with  this,  and  then  to  observe  whether  deflec- 
tion occurs  or  not ;  whether,  that  is,  with  the  arrange- 
ment selected  a  current  is  present  or  not.  But  the 
more  sensitive  is  the  multiplier,  the  harder  is  it  to 
connect  any  part  of  an  animal  with  it  in  such  a  way 
that  no  current  occm's,  and  it  would  be  a  mistake  to 
suppose  that  all  these  currents  are  elicited  by  the  ani- 
mal substances  themselves.  If,  for  example-,  the  ends 
of  the  wires  of  the  multiplier  are  connected  with  two 
wires  of  the  same  metal—  for  example,  copper ;  and  if 
these  wires  are  immersed  in  a  conducting  fluid — for 
example,  diluted  sulphuric  acid — considerable  deflection 
of  the  needle  always  occurs,  owing  to  the  fact  that  the 
copper  wires  are  never  so  homogeneous  that  they  do 
not  themselves  generate  a  slight  current.  If  platinum 
wires  are  used  instead  of  copper,  these  can,  it  is  true, 
be  rendered  homogeneous  by  careful  cleaning;  but  this 
homogeneity  soon  disappears,  so  that  even  with  this 
metal  currents  result  which  depend  solely  on  the  dis- 
similar nature  of  the  metallic  surfaces.     Fortimately, 


IfOMOGENEOUS   DIVERTING   VESSELS.  165 

there  are  combinations  of  metals  with  fluids  which  are 
free  from  these  faults.  Two  pieces  of  zinc,  the  surfaces 
of  which  have  been  amalgamated  by  smearing  with 
quicksilver — which  have,  therefore,  been  equally  covered 
with  a  coating  of  zinc-amalgam,  a  combination  of  zinc 
and  quicksilver — act  as  though  entirely  homogeneous  if 
they  are  immersed  in  a  solution  of  sulphate  of  zinc;  and 
these  metals  retain  their  homogeneity  even  when  elec- 
tric currents  traverse  the  metals  and  the  fluids.  The 
wire  of  the  multiplier  may  be  connected  with  strips  of 
amalgamated  zinc  of  this  sort,  and  these  may  be  im- 
mersed in  a  solution  of  sulphate  of  zinc  without  any 
deflection  being  indicated  even  by  a  very  sensitive  mul- 
tiplier. While,  therefore,  it  might  lead  to  serious  error 
if  the  wires  of  the  multiplier  were  brought  into  imme- 
diate contact  with  the  animal  substances  to  be  ex- 
amined— as  electricity  would,  in  such  case,  be  generated 
at  the  point  of  contact  itself — it  is  possible,  by  using 
this  amalgamated  zinc  and  solution  of  sulphate  of  zinc, 
to  exclude  any  foreign  source  of  electricity,  and,  pro- 
vided that  the  animal  tissue  is  properly  inserted,  to 
be  sure  that  the  observed  deflections  of  the  magnetic 
needle  are  really  due  to  electric  forces  situated  in  the 
animal  substances  themselves.  The  point  to  be  aimed 
at  in  this  experiment  is,  therefore,  to  place  the  animal 
substances  in  such  a  position  that  any  currents  gene- 
rated in  them  can  only  pass  to  the  wire  of  the  multi- 
plier through  the  zinc  solution  and  the  plates  of  amal- 
gamated zinc. 

6.  In  order  to  attain  this  object,  du  Bois-Reymond, 
to  whom  is  chiefly  due  our  knowledge  of  the  electric 
phenomena  of  animal  tissues,  arranged  the  apparatus 
in  the  following  way  (fig.  39).     The  ends  of  the  wires 


166 


PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 


of  the  multiplier  were  connected  with  two  troug-hs  or 
vessels  of  cast  zinc,  the  outer  surfaces  of  which  had 
been  lacquered,  while  the  inner  cavity  had  been  care- 
fully amalgamated.  A  solution  of  sulphate  of  zinc  was 
poured  into  this  cavity,  and  pads,  formed  of  many  folds 
of  blotting-paper  saturated  with  the  same  solution,  were 
folded  over  the  edge  of  the  vessels  in  such  a  way  that 


Fig.  39.    Hojiogeneous  mvERTixa  vessel,  as  used  by  E.  du  Bois- 
Keymond. 

part  was  immersed  in  the  solution,  part  protruded  over 
the  edges,  and  these  pads  end  in  a  sharply  cut  cross 
section.  Small  discs  of  an  isolating  substance  (vulca- 
nised india-rubber),  with  the  help  of  caoutchouc  bands, 
retained  the  pads  in  their  places.  The  vessels  being 
pushed  toward  each  other  till  the  pads  touched,  or  the 
intermediate  space  between  the  jmds  being  bridged  by  a 
third  pad,  also  saturated  with  a  solution  of  sulphate  of 
zinc,  the  needle  of  the  multiplier  continued  unmoved, 


ELECTROMOTIVE   FORCE.  167 

thus  afifording  proof  that  no  cause  of  the  generation  of 
currents  is  present  in  any  part  of  the  apparatus.  If  the 
body  to  be  examined  is  then  substituted  for  the  third 
pad,  with  the  result  of  deflecting  the  needle,  proof  is 
afforded  that  some  cause  effecting  the  generation  of  a 
current  exists  in  the  body.  The  only  disadvantage 
of  the  arrangement  is  that  the  animal  substances  thus 
examined,  being  in  contact  with  the  concentrated  solu- 
tion of  sulphate  of  zinc,  are  corroded,  and  their  vital 
qualities  are  injured.  To  avoid  this,  so-called  protec- 
tive shields,  i.e.  thin  plates  of  plastic  clay  (porcelain) 
which  has  been  mixed  with  a  diluted  solution  of  com- 
mon salt  (^  to  1  per  cent.),  are  used.  These  are  placed 
on  the  pads  of  blotting-paper,  where  the  tissue  to  be 
examined  touches  the  latter.  The  clay  protects  the 
tissue  from  direct  contact  with  the  solution  of  sulphate 
of  zinc,  though,  clay  being  a  conductor,  the  electric 
action  present  in  the  tissues  can  reach  the  zinc  and  the 
wires  of  the  multiplier. 

7.  In  examining  muscles  or  nerves  by  this  method, 
according  to  the  way  in  which  the  animal  substance  is 
applied,  sometimes  no  deflection  of  the  magnetic  needle 
is  observable,  sometimes  slight,  and  sometimes  stronger 
deflections  appear.  The  same  body,  for  example  a  piece 
of  muscle,  may  in  one  position  afford  a  very  strong  cur- 
rent, Avhile  in  another  position  it  affords  none  at  all. 
In  order  to  understand  this,  we  must  examine  the  way 
in  which  the  electric  currents  present  within  the  tissue 
examined  are  able  to  impart  themselves  to  the  wire  of 
the  multiplier,  in  the  case  of  the  method  of  experiment 
selected. 

Let  us  revert  to  the  simple  apparatus  (fig.  36,  p.  159), 
in  which  we  fii'st  studied  the  action  of  electric  currents 


168  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

on  a  magnetic  needle.  A  piece  of  zinc  and  a  piece  of 
copper  are  immersed  in  diluted  sulphuric  acid,  their 
projecting  edges  being  connected  bj  a  piece  of  wire. 
When  in  this  condition  the  apparatus  is  said  to  be  closed. 
Within  it  circulates  a  cmrent  which  passes  within  the 
wire  from  the  copper  to  the  zinc,  and  within  the  fluid 
from  the  zinc  to  the  copper.  If  the  closing  wire  is 
observed  by  itself,  no  current  arises  in  it  until  it  is 
joined  to  the  apparatus.  And  if  the  apparatus  is  ob- 
served by  itself,  that  is,  without  the  closing  wire,  there 
is  no  current  present  in  it.  It  is  only  in  a  closed  circle 
that  a  current  can  be  generated.  It  is,  however,  in  the 
apparatus  that  the  cause  which  imder  favourable  cir- 
cumstances gives  rise  to  the  electric  current,  lies ;  for  if 
the  wire  by  itself  is  bent  into  a  circle  no  current  is 
generated  within  it.  Even  the  cause  of  the  generation 
of  currents  within  the  apparatus  may  be  shown.  If  when 
the  apparatus  is  open,  that  is,  when  the  circuit  is  not 
completed  by  the  addition  of  the  connecting  wire,  the 
projecting  edges  of  the  copper  and  zinc  are  connected 
with  an  electrometer,  the  gold  leaflets  are  seen  to  di- 
verge, thus  showing  that  an  electric  tension  prevails 
at  these  metallic  ends  projecting  from  the  fluid.  This 
tension  is  positive  at  the  copper  end,  negative  at 
the  zinc  end.  On  connecting  the  two  metals  by  a 
closing  wire,  the  opposed  electric  currents  unite,  and 
this  is  the  cause  of  the  current  in  the  wire.  The  force 
which  within  the  wire  exhibited  electric  tension  con- 
tinues to  act,  and  causes  the  current  to  continue  to 
traverse  the  wire.  This  is  called  the  electromotive  force 
of  the  apparatus.  It  expresses  itself,  when  the  apparatus 
is  not  closed,  in  the  electric  tension  at  the  projecting 
metallic  ends  or  poles  of  the  apparatus ;  and  when  the 


ELECTROMOTIVE    FORCE.  169 

poles  are  connected  together  by  a  closing  arch,  it  finds 
expression  in  the  current  which  it  generates  in  this 
arch. 

Supposing  that  the  two  metals  contained  in  the 
fluid  did  not  protrude  from  the  latter,  but  were  in 
contact  with  each  other  within  the  fluid,  then  it  is 
evident  that  the  apparatus  would  be  closed  in  this  case 
also,  but  the  closing  arch  would  then  lie  within  the 
fluid.  Through  this  the  current  must  pass  from  the 
copper  to  the  zinc,  and  from  the  zinc  to  the  copper 
through  the  fluid.  That  this  is  really  the  case  can 
easily  be  shown,  for  on  the  immersed  metallic  surfaces 
globules  are  seen  to  be  generated,  due  to  the  gases 
generated  by  the  electric  current  by  the  separation  of 
the  water  into  its  constituent  parts,  hydrogen  being 
found  at  the  copper,  oxygen  at  the  zinc  point.  In  this 
case,  therefore,  the  apparatus  is  in  itself  closed.  No 
external  closing-arch  is  present,  the  existence  of  a  mag- 
netic current  at  which  can  be  indicated  by  means  of  a 
magnetic  needle.  Yet  with  a  multiplier  it  is  possible 
to  show  the  currents  circulating  in  the  fluid,  and  in 
the  immersed  metals  ;  this  may  be  done  by  a  principle 
spoken  of  as  the  distribution  of  electric  currents. 

Let  us  assume  that  an  apparatus  h  is  not  directly 
closed  by  a  closing-arch,  but  that  from  each  pole  passes 
a  wire  which  touches  the  conductor,  the  form  of  which 
does  not  matter,  shown  in  fig.  40  at  two  points,  A  B. 
It  can  be  shown  that  the  electric  currents  pass  in  this 
case  through  the  body,  but  distribute  themselves,  not 
merely  in  straight  lines  connecting  A  and  J5,  but 
throughout  the  body,  so  that  they  represent  a  number 
of  lines  of  conduction,  all  of  which  meet  together  at 
the  points  A  and  5,  where  the  electric  currents  enter 


170 


PHYSIOLOGY  OF  MUSCLES  AXD  NERVES. 


and  leave  the  body.  If  the  body  which  is  inserted  is  of 
simple  form,  the  separate  lines  of  transmission  may  easily 
be  calculated  from  the  form:  in  bodies  of  irresrular 
shape  this  is  somewhat  hard  to  do,  but  even  in  such 
cases  it  is  possible  to  determine  experimentally,  not  only 
that  the  electricity  distributes  itself  throughout  the 
body,  but  even  the  lines  along  which  the  separate  cur- 
rents pass. 

Taking  a  simple  example,  for  instance,  a  thick  cyl- 
indrical rod,  in  which   the  electricity  passes  in  at  the 


Fig.  40.     Distribution  of  the  currents  ix  irregular  conductors. 

surface  of  one  end  and  out  at  the  other,  it  is  prima  facie 
probable  that  the  lines  simply  traverse  the  length  of 
the  rod  parallel  to  its  axis.  We  may  in  imagination 
replace  the  rod  by  a  bundle  of  wires,  each  of  which  will 
in  this  case  be  traversed  by  a  portion  of  the  whole 
ciu-rent.  If  one  of  these  wires  is  cut,  and  its  ends  are 
connected  with  the  multiplier,  it  is  evident  that  that 
part  of  the  current  which  traverses  this  wire  must 
pass  to  the  multiplier  and  cause  a  deflection  of  the 
needle.     But  even  if  the  wire  is  not  cut.  but  is  con- 


ELECTRIC    'fall.'  171 

nected  with  the  multiplier  at  two  points  in  its  length, 
in  this  case  also  a  part  of  the  current  must,  in  ac- 
cordance with  the  law  of  the  distribution  of  currents, 
branch  off  through  the  multiplier. 

8.  This  may  be  made  intelKgible  in  another  way. 
"We  saw  that  a  certain  electric  tension  exists  at  the  poles 
of  an  open  apparatus,  and  that  the  opposed  tensions 
of  the  two  poles  are  the  causes  of  the  current  in  the 
closing  wire.  If  the  poles  were  but  once  charged  with 
proper  quantities  of  electricity,  these  would  unite  in 
the  wire,  with  the  result  of  producing  an  instantaneous 
current.  But  as,  in  consequence  of  the  electromotive 
force  of  the  apparatus,  the  tension  at  the  poles  is  con- 
tinually renewed,  the  current  is  continuous.  So  that  at 
both  ends  of  a  closing  wire  opposed  tensions  prevail  con- 
stantly, and  these  act  on  the  natural  electricity  present 
in  the  wire,  as  in  every  other  body,  and  set  it  in  motion. 
Consequently,  while  the  current  flows  through  the  wire, 
different  tensions  must  prevail  at  the  various  points  of 
the  wire.  At  the  point  of  contact  with  the  positive 
pole  there  is  a  definite  positive  tension ;  at  the  point 
of  contact  with  the  negative  pole  there  is  a  similar 
negative  tension,  and  in  the  middle  of  the  wire  there 
must  be  a  point  at  which  the  tension  =  0.  This  may 
be  diagrammatically  shown  by  representing  the  tension 
which  prevails  at  each  point  of  the  wire  by  a  line  de- 
scribed at  right  angles  to  the  wire,  the  length  of  which 
represents  the  tension  proper  to  the  point  in  case.  Let 
a  h  (fig.  41)  be  the  wire;  then  the  line  a  c  is  the  ex- 
pression of  the  tension  existing  at  one  of  its  ends, 
which  is  connected  with  the  positive  pole.  In  order 
to  indicate  that  the  tension  at  the  other  end,  b,  is 
negative,  i  e.  of  an  opposite  kind,  let  the  line  b  d  he 


172  PHYSIOLOGY    OF    MUSCLES    AND    NEEVES. 

drawn  downward  from  a  h.  In  the  centre  there  is  no 
tension.  At  any  point  between  the  middle  and  the 
end  a,  say  at  e,  a  positive  tension  must  prevail  which  is 
less  than  that  at  a,  but  greater  than  0.  It  is  expressed 
by  the  line  e  f.  Similarly  at  any  point  between  the 
middle  and  the  end  b,  say  at  g,  there  is  a  definite 
negative  tension  which  may  be  expressed  by  the  line 
g  h.-  The  same  thing  may  be  done  for  each  of  the 
other  points  in  the  wire.  If  the  wire  is  quite  uniform, 
the  positive  tension  decreases  quite  regularly  from  the 
end  a  to  the  middle,  and  in  the  same  way  the  nega- 
tive tension  decreases  quite  regularly  from  the  end  h 
to  the  middle.     Unitins:  the  ends  of  the  lines  which 


Fig.  4L    The  fall  ix  the  electkicity. 

thus  express  the  tensions,  the  result  is  an  oblique 
straight  line  which  cuts  the  wire  in  the  centre,  and 
the  distance  of  which  from  the  wire  at  any  point  re- 
presents the  tension  at  that  point. 

This  regular  decrease  in  the  tensions  prevailing  in 
the  wire  may  be  shown  by  means  of  an  electrometer,  if 
the  latter  is  brought  into  contact  with  each  point  in 
the  wire.  The  gradual  decrease  of  the  tensions  in  the 
wire  is  evidently  also  the  essential  cause  of  the  move- 
ment of  the  electricity  through  the  wire,  for  at  each 
point  in  the  wire  there  are  adjacent  portions  in  which 
the  tensions  gradually  become  less  from  left  to  right, 
so  that  the  electricity  is  enabled  to  flow  from  left  to 
right.  The  case  is  evidently  like  that  of  a  tube  through 


ELECTRIC    'FALL. 


173 


which  water  flows,  for  in  that  case  also  the  pressure  of 
the  water  gradually  and  regularly  decreases  from  one 
end  to  the  other.  To  express  this  similarity  we  will 
apply  to  electric  currents  a  term  borrowed  from  flowing 
liquids,  and  will  call  the  gradual  decrease  in  the  tension 
the  fall  ill.  the  electricity. 

Let  us  compare  two  wires  of  the  same  thickness, 
but  of  unequal  length,  a  b  and  c  d  (fig.  42).  If  a  b 
is  inserted  between  the  poles  of  a  chain,  the  fall  is 
represented  by  the  oblique  line  e  f.     Supposing  a  b 


Fig.  42.    The  electric  fall  ix  uiFFEiiEXT  wires. 


removed,  and  c  d  inserted  between  the  poles  of  the 
same  chain,  the  tensions  at  the  ends  would  be  the  same, 
so  that  the  fall  in  the  ease  of  the  wire  c  d  may  be 
represented  by  the  oblique  line  rj  h.  It  will  be  ob- 
served that  in  the  case  of  the  shorter  wire  the  line  runs 
much  more  abruptly,  the  fall  is  greater,  and  the  cur- 
rent of  electricity  advances  much  more  rapidly  in  this 
wire.  Assuming  now  that  the  two  wires  a  b  and  c  d 
are  simultaneously  attached  to  the  poles  of  the  chain, 
in  this  case  also  the  tensions  at  the  two  ends  must  be 
equal,  but  the  fall  must  be  different.     Supposing  that 


174  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

instead  of  these  two  wires  a  number  of  separate  wires 
are  used,  then  the  same  thing  happens ;  and  if  the  wires 
are  welded  together  into  a  common  conducting  body, 
this  does  not  essentially  alter  the  conditions  of  the  fall, 
so  that  we  may  imagine  the  whole  body  to  consist  of 
these  separate  wires,  in  each  of  which  a  definite  fall, 
the  steepness  of  which  depends  on  the  length  of  the 
particular  wire,  prevails.  These  wires  are,  however, 
merely  paths  along  which  the  electric  currents  pass, 
and  of  which  we  have  already  spoken.  In  the  case 
of  these  paths  also  definite  falls  must  prevail,  and  these 
must  be  more  steep  in  proportion  as  the  points  at 
which  the  electric  currents  enter  and  make  their  exit 
are  nearer  together. 

9.  Let  us  return  to  the  case  of  a  simple  wire 
through  which  a  current  passes.  On  uniting  two 
points  in  this  with  two  electrometers,  these  exhibit 
varying  tensions,  and  the  difference  is  greater  the  fur- 
ther the  two  points  are  separated  from  each  other.  If 
the  points  are  then  connected  by  a  bent  wire,  it  is 
evident  that  the  different  tensions  at  the  points  of 
contact  must  effect  a  disturbance  in  the  natural  elec- 
tricity within  the  applied  wires,  and  consequently  must 
generate  an  electric  current  from  the  point  at  which 
the  tension  is  greater  to  that  at  which  it  is  less.  If  a 
multiplier  is  inserted  in  the  applied  wire,  the  needle 
will  be  deflected.  This  is  as  true  of  a  regular  as  of  an 
irregular  conductor.  If  in  the  body  A  B  (fig.  43), 
electricity  moves  along  various  paths,  and  if,  as  we 
have  seen,  different  tensions  prevail  at  two  points  in 
such  a  path,  a  current  must  arise  if  the  ends  of  a  bent 
wire  are  applied  to  these  points,  and  if  the  bent  wire 
is  supplied  with  a  multiplier  the  needle  will  be  de- 


TENSION    IN    THE    ARCH. 


175 


fleeted.  On  the  other  hand,  in  two  different  paths  of 
conduction  there  must  always  be  points  at  which  the 
tension  is  the  same.  For  in  each  path  the  tension 
begins  at  a  certain  positive  value  (at  A),  and  passes 
through  a  value  =  0  to  a  certain  negative  value  (at  _B). 
The  needle  of  the  multiplier  must,  therefore,  remain  at 
rest  if  the  two  ends  of  the  wire  of  the  multiplier  are 


Fig.  43.     Paths  of  eli:ctkicity  in  a  conductor. 

applied,  not  to  two  points  of  different  tension,  but  to 
two  points  of  equal  tension.  This  enables  us  to  ob- 
serve whether  in  any  body  in  which  electric  currents 
move  in  any  form,  two  points  have  similar  or  dissimilar 
tension,  and  by  systematic  experiments  of  this  kind  we 
shall  evidently  gradually  obtain  an  insight  into  the 
form  and  relative  position  of  the  paths  of  conduction 
within  the  body  examined. 


176  FHYSIOLOGy    OF   JVEKVES   AND    MUSCLES. 


CHAPTEE   X. 

1.  Diverting-  arclies  ;  2.  Current-curves  and  tension-curves  ;  3.  Di- 
verting cylinders;  '4.  Method  of  measuring  tension  dififerences 
by  compensation, 

1.  If  the  two  ends  of  a  bent  wire  are  ajDplied,  in 
the  way  described  in  the  last  chapter,  to  any  conductor 
which  is  traversed  by  currents,  then  part  of  the  currents 
present  in  the  conductor  may  flow  through  this  wire. 
Part  of  the  current  is,  as  it  were,  conducted  out  of  the 
body  in  order  to  facilitate  its  examination.  Under 
certain  circumstances  this  may  cause  an  alteration  in 
the  conditions  of  the  currents  within  the  conductor. 
We  will,  however,  assume  that  this  is  not  the  case, 
but  that  the  tensions  at  the  points  at  which  the  wire 
is  applied  to  the  conductor  are  not  altered.^  The 
direction  and  strength  of  the  current  which  arises  in 
the  conductor  will  then  depend  only  on  the  differences 
in  tension  at  the  point  of  contact,  and  on  the  resistance 
offered  by  the  wire. 

A  wire  of  this  sort  applied  to  a  conductor  traversed 
by  currents  is  called  a  diverting  arch ;  the  ends  of  the 
wire  with  which  it  touches  the  body  to  be  examined 
are  called  the  feet  of  the  arch;  and  the  distance  be- 
tween these  feet  is  called  the  distance  of  tension. 

*  Tlie  circumstances  under  whicli  tlie  exceptions  occur  cannot 
be  explained  here  ;  yet  matters  may  be  so  arranged  that  such  excep- 
tions do  occur. 


CURRENT-CURVES   AND   TENSION-CURVES.  177 

The  further  nature  of  the  arch  does  not  matter. 
It  may  consist  of  one  or  more  wires,  and  it  may  or 
may  not  include  moist  conductors.  Only  one  condition 
must  be  fulfilled  :  no  electric  actions  must  be  caused 
by  the  contact  of  the  diverting  arch  with  the  conductor 
which  is  to  be  examined.  Now,  we  have  already  seen 
that  this  is  unavoidable  wben  metalHc  wires  are  ap- 
plied to  moist  animal  substances.  The  ends  of  the 
wire  of  the  arch  must,  therefore,  be  connected  with  the 
zinc  diverting-vessels  described  above  (fig.  38).  In 
this  arrangement  the  clay  shields,  satm-ated  with  a 
salt-solution,  represent  the  feet  of  the  diverting  arch. 
Such  an  arch,  which  neither  in  itself  nor  by  its  appli- 
cation to  the  conductor  under  examination  affords  any 
cause  for  the  generation  of  currents,  is  an  homogeneous 
arch. 

In  order  to  attain  a  thorough  knowledge  of  the 
distribution  of  tensions  in  a  conductor,  it  would  ap- 
parently be  necessary  to  touch  all  points  of  the  latter 
in  turn  with  the  feet  of  the  diverting  arch.  This  is 
easily  done  in  the  case  of  the  surface  of  the  body,  but 
as  regards  the  inner  parts  it  is  hard  and  often  imprac- 
ticable. We  must  therefore  rest  satisfied  with  an 
examination  of  the  surface ;  but  it  may  be  shown  that 
trustworthy  conclusions  as  to  the  character  of  the  inner 
parts  may  be  drawn  from  this  study  of  the  surface. 

2.  Two  cases  must  be  distinguished.  Either  the 
body  to  be  examined  is  in  itself  incapable  of  electric 
action,  and  the  electric  currents,  the  internal  distri- 
bution of  which  is  to  be  examined,  are  imparted  to 
it  from  external  sources ;  or  electromotive  forces  are 
situated  within  the  body  itself,  and  it  is  the  currents 
generated  by  these  which  form  the  object  of  research. 
9 


178 


PHYSlOLOGrY    OF   MUSCLES    AND    NERVES. 


The  ease  of  organic  tissues,  with  which  we  are  con- 
cerned, is  of  the  latter  sort ;  for  we  have  seen  that 
■when  these  are  inserted  between  the  ends  of  a  homo- 
geneous arch,  electric  action  takes  place  under  certain 
circumstances.  The  fact  that  in  other  cases  no  such 
action  occurs  will  be  intelligible  after  the  account  just 
given,  for  we  may  assume  that  in  such  cases  the  two 
points  which  are  touched  by  the  ends  of  the  arch  are 
similar  in  tension. 

Let  BODE  (fig.  44)  represent  a  section  through 
E  = ^D 


Fig.  44.  Currext-cuuves  and  texsiox-cuuves. 
a  body  in  which  an  electromotive  force  is  present.  For 
the  sake  of  simplicity  we  will  assume  that  the  body 
is  a  regular  cylinder,  and  that  the  electromotive  force 
is  situated  in  its  axis;  then  that  which  we  show  in 
the  case  of  BODE  will  be  equally  true  of  every 
other  section.  Let  the  point  A  represent  the  seat  of 
electromotive  force  ^  which  sets  the  positive  electricity 
in  motion  toward  the  right,  the  negative  electricity 
toward  the  left.    The  whole  body  is  then  occupied  by 

^  In  order  to  have  a  physical  basis  for  this  electromotive  force  we 
may  imagine  the  cylinder  to  consist  of  a  fluid,  and  that  at  the  point 
^1  is  situated  a  body  consisting  half  of  ziEc,  half  of  copper. 


CDRREXT-CURVES   AXD   TEXSION-CURVES.  179 

current-paths.  We  naturally  think  of  these  paths 
within  the  cylinder  as  planes,  so  that  we  obtain  current- 
planes,  which  enclose  each  other  like  the  scales  of  an 
onion,  and  which  in  the  section  which  we  figure  form 
closed  curves  all  of  which  pass  through  the  point  A. 
They  are  represented  on  the  figure  by  unbroken  lines. 
On  each  of  these  paths  a  definite  fall  prevails,  as  we 
know — that  is,  in  each  of  these  the  point  immediately 
on  the  right  nearest  to  J.  is  the  most  positive,  the  ten- 
sion gradually  decreasing  toward  and  up  to  the  middle, 
where  it  =  0,  then  becomes  negative,  the  greatest 
negative  tension  being  immediately  next  to  A  on  the 
left.  This  is  true  of  all  paths  or  lines  of  conduction. 
In  each  there  is  a  point  at  which  the  tension  =  0 ;  on 
the  right  of  this  the  tension  =  +  1 ;  yet  further  to  the 
right  it  =  +2,  and  so  on  up  to  the  greatest  tension  at 
A  ;  and  similarly  in  each  curve,  to  the  left  of  the  zero 
point  there  are  points  at  which  the  tension  =  —  1, 
—  2,  and  so  on.  If  all  the  points  of  equal  tension  are 
united,  the  result  is  a  second  system  of  curves,  which 
are  at  right  angles  to  the  current  curves,  and  which  are 
represented  in  our  figure  by  dotted  lines.  There  is  a 
curve  which  unites  all  points  at  which  the  tension  =  0, 
another  which  unites  those  points  at  which  the  tension 
=  +  1,  and  so  on.  These  maybe  called  tension-curves 
or  iso-electric  curves.  In  the  cylinder  the  section  of 
which  is  here  drawn,  these  curves  evidently  represent 
planes  which  cut  the  planes  of  the  currents  already 
mentioned,  and  which  may  be  called  tension-planes  or 
iso-electric  surfaces.  On  the  outside  of  the  cylinder 
these  iso-electric  surfaces  are  exposed,  and  meet  the 
surface  in  bent  lines,  which  in  the  simple  figure 
which  lies  before  us  are  all  parallel,  that  is,  surfaces 


180  PHYSIOLOGY    OF    MUSCLES    AND   NERVES. 

wh-ich  cut  the  surfaces  of  the  cylinder  parallel  to  the 
surfaces  of  its  ends.  The  iso-electric  surface  repre- 
senting a  tension  =  0,  cuts  the  cylinder  near  its  centre, 
and  divides  it  into  two  unequal  halves,  of  which  the 
right  is  positive,  and  the  left  negative.  The  other  iso- 
electric curves  cut  the  surfaces  of  the  cylinder  in  par- 
allel curved  lines;  and  the  iso-electric  curves  repre- 
senting the  greatest  positive  and  the  greatest  negative 
tensions  meet  the  surfaces  at  the  central  points  of  the 
end  surfaces  of  the  cylinder  which,  in  the  figure  given, 
are  marked  +  b  and  —  b. 

The  conditions  are  not  always  as  simple  as  in  this 
case.  If  the  body  under  examination  is  not  a  re- 
gular cylinder,  and  if  the  electromotive  force  is  not 
situated  exactly  in  its  axis,  then  the  arrangement  of 
the  iso-electric  surfaces  is  more  complex.  The  body 
under  examination  is,  however,  always  occupied  by  a 
system  of  current-planes  inserted  one  within  the  other, 
and  a  system  of  iso-electric  sm-faces  can  be  constructed 
which  cut  the  outer  sm-faces  of  the  body  in  curves  of 
one  form  or  another.  Along  each  curve  of  the  outer 
surface  corresponding  with  an  iso-electric  surface  the 
same  tension  always  prevails  ;  on  two  of  these  curves  if 
adjacent  the  tensions  always  differ.  Eegarding  therefore 
only  the  siurface,  it  may  be  said  that  if  an  electro- 
motive force  is  present  within  the  body,  this  must  cor- 
respond with  a  definite  arrangement  of  tensions  on 
the  surface  of  the  body.  By  studying  this  superficial 
arrangement  of  the  tensions  we  may  therefore  draw 
conclusions  from  this  as  to  the  situation  of  the  electro- 
motive force  within  the  body. 

3.  The  diverting  vessels  (fig.  38)  above  described 
are  not  always  sufficient  for  the  purposes  of  research. 


DIVERTING    CYLINDERS. 


181 


Apart  from  the  fact  that  the  insertion  of  the  animal 
substances  between  the  pads  cannot  always  be  con- 
veniently managed,  it  is  impossible  to  bring  individual 
points  of  the  substance  into  contact  with  the  pads.  This 
does  not  matter  at  all  when  the  i so-electric  curves  run 
parallel  to  each  other,  as  in  the  case  described  in  §  2, 
on  the  outer  surface  of  the  cylinder.  In  such  cases  it 
is  always  sufficient  to  apply  the  sharp  edges  of  the  clay 
discs  to  the  surface  in  such  a  way  that  all  the  points 
which  come  in  contact  with  these  edofes  belong-  to  the 
same  iso-electric  curve.     But  even  in  observations  on 


l';.,.  1, 


lM\i;i;TIN(i    (  YLINDEnS   AS   USED    BY    E.   DU    BoIS  ReVJIOXD. 


the  surfaces  of  the  ends  of  the  cylinder  the  case  is  dif- 
ferent. Here  the  iso-electric  curves  form  concentric 
circles.  In  such  cases  it  is  absolutely  necessary  to 
carry  out  with  somewhat  greater  accuracy  the  theoretic 
condition  that  the  diverting  arch  should  touch  the 
conductor  which  is  to  be  examined  at  two  points.  An- 
other form  of  diverting  apparatus,  invented  by  du 
Bois-Roymond,  is  used  both  for  this  purpose  and  for 
conducting  currents  to  the  body  under  examination  in 
cases  where  it  is  important  to  avoid  electrical  polari- 
sation. These,  which  are  usually  called  unpolaris- 
ahle  electrodes,  are  represented  in  fig.  45.     The  glass 


182  PHYSIOLOGY   OF    MUSCLES    AND   NERVES. 

cylinder  a,  somewhat  flattened,  is  attached  to  the  stand 
A.  The  socket  e  and  the  motor  apparatus  on  the 
column  h  allow  the  glass  cylinder  to  be  placed  in  any 
desired  position.  Within  the  cylinder  is  a  strip  of 
amalgamated  sheet  zinc  6,  which  can  be  connected 
with  the  multiplier  by  means  of  a  wire.  The  glass 
cylinder  is  closed  below  with  a  stopper  of  plastic  clay 
moistened  with  a  solution  of  common  salt,  the  project- 
ing ends  of  which  can  be  moulded  into  a  point  which 
touches  the  smallest  possible  point  on  the  conductor 
to  be  examined.  The  space  within  the  glass  cylinder 
is  filled  with  a  concentrated  solution  of  sulj)hate  of 
zinc,  and  thus  forms  an  unpolarisable  and  homogene- 
ous conductor  between  the  strip  of  zinc  and  the  clay 
point.  A  second  and  exactly  similar  apparatus,  which 
is  only  partly  represented  in  the  figure,  provides  for 
the  diversion  from  the  other  point  of  the  conductor. 

Whatever  form  of  diverting  apparatus  is  employed, 
the  determination  of  the  fact  whether  the  two  points 
touched  by  the  feet  of  the  diverting  arch  have  like  or 
unlike  tension  will  be  more  accurate  the  more  sensi- 
tive is  the  multiplier  which  is  inserted  in  the  diverting 
arch.  By  placing  the  body  to  be  examined  in  such  a 
way  that  the  various  points  in  its  surface  successively 
lie  on  the  pads  of  the  above-described  diverting  vessel 
(see  ch.  ix.  §  5),  or  by  touching  them  with  the  ends  of 
the  diverting  cylinder  just  mentioned,  it  may  be  dis- 
covered which  points  have  equal  tension  (for  in  such 
cases  the  multiplier  will  indicate  no  deflection),  or,  if  the 
points  touched  are  unequal  in  tension,  it  may  be  dis- 
covered at  which  the  positive  tension  is  greatest.  For, 
from  this  latter  point  a  current  must  pass  through  the 
multiplier  to  the  point  at  which  the  positive  tension  is 


MEASUREMENT    OF    DIFFERENCES    OF   TENSION.       183 

less  (or,  in  other  words,  the  negative  tension  is  greater), 
a  fact  which  can  be  recognised  by  the  direction  of  the 
deflection  exhibited  by  the  multiplier.  In  order,  how- 
ever, thoroughly  to  understand  the  position  of  the  iso- 
electric curves,  it  would  also  be  necessary  to  know  the 
absolute  amount  of  the  iso-electric  tension  at  each 
point.  Instead  of  this,  however,  it  is  sufficient  to  de- 
termine the  difference  between  the  tensions  at  each 
two  points,  which  may  be  found  by  very  accurate  and 
trustworthy  methods.^ 

4.  To  calculate  these  differences  from  the  extent  of 
the  deflection  of  the  multiplier  would,  for  reasons  which 
cannot  here  be  further  explained,  be  very  inconvenient 
and  would  afford  very  inaccurate  results.  But  these 
differences  may  be  measured  with  quite  sufficient  pre-  • 
cision  by  a  method  invented  by  Poggendorflf  and  after- 
wards improved  by  du  Bois-Eeymond. 

If  it  is  required  to  determine  the  weight  of  any 
body,  the  latter  is  placed  in  one  of  a  pair  of  scales, 
and  weights  are  placed  in  the  other  until  the  two  are 
again  in  equilibrium.  As  in  this  case  the  action  of 
the  two  weights  on  the  beam  of  the  scales  is  to  raise 
each  other  up,  they  must  be  equal.  This  well-knoAvn 
principle  is,  however,  capable  of  an  important  generali- 
sation. It  is,  for  example,  required  to  determine  the 
attraction  exercised  by  a  magnet  on  a  piece  of  iron. 
The  iron  is  attached  to  one  end  of  the  beam  of  the 
scales,  weights  to  the  other,  till  the  beam  is  again 
balanced.  The  magnet  being  then  placed  under  the 
iron,  the  balance  of  the  beam  is  again  disturbed  by  the 
magnetic  attraction,  and  weight  must  be  added  to  the 
other  scale  before  it  is  restored.  It  is  evident  that  the 
'  See  Notes  and  Additions,  No.  10. 


184 


PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 


amount  of  weight  required  for  this  latter  purpose  affords 
a  measure  of  the  force  of  attraction  between  the  iron 
and  the  magnet. 

In  the  present  case  a  certain  deflection  in  the  multi- 
plier results  from  the  difference  in  tension  at  the  feet 
of  the  diverting  arch.  It  is  required  to  measure  the 
difference.  If  it  is  in  any  way  possible  to  influence  the 
deflection  of  the  muItipKer  in  an  opposite  direction,  and 
exactly  to  such  a  degree  that  the  multiplier  no  longer 
indicates  any  deflection,  then  the  two  influences  must 


Fig.  46.    Measurement  by  compexsatiox  of  the  difference  of 

TENSION. 

be  equal,  and  the  one  may  serve  as  a  measure  for  the 
other.  The  experiment  indicated  in  these  instances 
is  called  measurement  by  compensation.  In  order  to 
apply  it  to  the  case  in  point,  the  action  of  one  dif- 
ference of  tension  is  cancelled  by  that  of  another  which 
may  be  altered  at  will.  The  rheochord,  Avhich  has  al- 
ready been  described,  affords  a  convenient  means  of 
doing  this. 

Let  R  R'  (fig.  46)  be  a  wire  extended  in  a  straight 
line  (the  line  of  the  rheochord)  through  which  a  current  is 


MEASUREMENT   OF   DIFFERENCES   OF   TENSION.      185 

passed  from  the  apparatus  K.  TF  indicates  an  arrange- 
ment by  which  the  current  of  this  apparatus  may  be 
made  to  pass  as  desired  either  from  R  to  R'  or  in  the 
opposite  direction.  T  is  a  multiplier  by  the  deflection 
of  which  proof  may  be  obtained  that  the  current  of  this 
apparatus  remains  constant  in  its  strengih.  The  other 
parts  given  in  the  figure  we  will  for  the  present  dis- 
regard. According  to  what  we  have  already  seen  (ch. 
ix.  §  7)  a  definite  electric  fall  must  be  present  in  the 
rheochord.  Let  us  assume  that  the  current  passes  from 
R'  to  jR,  that  the  tension  at  R  =  0,  and  that  it  in- 
creases toward  R'.  As  the  rheochord  line  is  entirely 
homogeneous,  this  increase  must  take  place  quite  regu- 
larly ;  i.e.  the  tension  at  every  point  of  the  chord  must 
be  proportionate  to  the  distance  of  that  point  from  R. 
Now  let  us  imagine  that  a  body,  A  B,  within  which 
an  electromotive  force  is  present,  is  to  be  examined. 
Naturally  two  points  on  its  surface,  a  and  b,  have  dif- 
ferent tensions,  and  it  is  this  difi'erenee  which  is  to  be 
measured.  The  point  a  must  be  united  by  means  of  a 
wire  (in  which  is  inserted  as  sensitive  a  multiplier  as 
possible)  with  i? ;  the  point  b  must  be  connected  by  a 
wire  with  a  sliding-piece  S  which  moves  on  the  rheo- 
chord line.  Two  ditferences  of  tension  now  act  on  the 
multiplier.  Firstly,  the  differences  of  tension  between 
the  points  R  and  S  of  the  rheochord;  and,  secondly, 
that  between  the  points  a  and  b.  If  at  6  there  is  a 
greater  positive  tension  than  at  a,  then  the  two  dif- 
ferences  of  tension   are    opposed   in  action.'     As  the 

'  If  the  positive  tension  were  greater  at  a  than  at  b,  then  it 
would  be  necessary  to  reverse  the  direction  of  the  current  within 
the  rhecohord.  The  commutator  W  is  therefore  inserted  to  effect 
this  reversal  of  the  current. 


186  PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 

difference  in  tension  between  R  and  S  can  be  altered 
by  changing  the  position  of  8,  the  slide  S  may  be 
placed  in  such  a  position  that  the  two  influences  exactly 
balance  each  other,  or,  in  other  words,  in  such  a  position 
that  the  multiplier  indicates  no  deflection.  Thus  it  is 
evident  that 

S  -  R  -  1}  -  a  =  0 

Difference  in  tension  at  the  Difference  in  tension  at 

two  points  of  the  I'lieochord.  the  two  points  of  the  con- 

ductor. 

ov  S  -   R   =   d   -   a\ 

the  difference,  that  is,  of  the  tension  between  6  and  a 
is  equal  to  the  difference  of  tension  between  8  and  R. 


Fig.  47.    Du  Bois-Reymoxd's  round  compensator. 

The  latter  is  expressed  in  millimetres,  each  of  which 
indicates  a  certain  constant  amount  Avhen   a  definite 
rheochord  wire  is  used,  and  when  the  current  which  is 
conducted  through  the  latter  is  of  a  definite  strength. 
To  facilitate  measurements  of  this  kind,  du  Bois- 


MEASUREMENT    OF    DIFFERENCES    OF    TENSION. 


187 


Eejmond  invented  a  'round  compensator'  (fig  47),  in 
wliich  the  wire  of  the  rheochord  r  r'  is  placed  on  the  cir- 
cumference of  a  circular  disc  of  vulcanised  india-rubber. 
The  beginnino-  and  the  end  of  the  wire  are  connected 


Fig.  48.   Diaguam  <n-  ELEcrnic  MEAsvnKMii.Nx  nv  sieassof  a  uound 

COMPENSATOR. 


with  the  clamps  I  and  II ;  from  the  beginning  a  wire 
also  passes  to  the  clamp  IV.  The  clamp  III  is  con- 
nected   with    the   small    reel   r,   which  is    pressed    by 


188  PHYSIOLOGY   OF   MUSCLES   AND   NERVES. 

a  spring  against  the  wire,  and  replaces  the  slide.  By 
turning  the  disc  the  length  of  the  inserted  portion  of 
the  rheochord  is  altered. 

The  whole  arrangement  is  shown  more  clearly  in 
tig.  48,  which  may  at  the-  same  time  serve  as  a  diagram 
of  the  experiments  with  muscles  and  nerves,  to  which 
we  are  now  about  to  turn  our  attention.  N  r'  r  S  is  the 
circular  rheochord  wire,  through  which  the  current  of 
the  measuring  apparatus  passes  in  the  direction  of  the 
arrow  ;  yu.  is  a  muscle,  two  of  the  points  on  the  outer 
surface  of  which,  being  connected  with  the  multiplier, 
afford  a  current,  which  is  exactly  compensated  by  that 
portion  of  the  current  which  branches  off  from  the 
rheochord  at  the  points  r  and  o.  The  particular  length 
o  r  of  the  rheochord  wire  at  which  this  exact  compen- 
sation is  accomplished,  indicates  according  to  the  fixed 
standard  (the  degree  of  compensation)  the  difference  in 
tension  at  the  particular  points  on  the  muscle  which  are 
tested.  This  length  may  be  found  by  turning  the  round 
disc,  together  with  the  platinum  wire,  until  the  mul- 
tiplier no  longer  indicates  any  deflection.  By  means 
of  a  magnifying  glass,  the  length  of  the  inserted  wire, 
from  its  commencement  at  o  to  the  reel  at  r,  can  be 
read  off  on  a  graduated  scale. 


CHAPTER  XI. 

1.  A  regular  muscle-prism  ;  2.  Currents  and  tensions  in  a  muscle- 
prism;  3.  Muscle-rhombus;  4.  Irregular  muscle- rhombi ;  5.  Cur- 
rent of  m.  gastrocncmii(s. 

1 .  Beginning  the  study  of  the  electric  phenomena 
exhibited  in  animal  tissues  with  muscles,  we  will  at  first 
experiment  only  with  single,  extracted  muscles.  Even 
these,  however,  exhibit  phenomena  so  complex  in  some 
respects,  that  it  will  be  better  to  take  first  a  compara- 
tively simple  case.  In  taking  one  not  exactly  under 
natural  conditions— if,  that  is,  we  use  a  muscle  artifi- 
cially prepared  for  the  purpose  of  experiment — this  pro- 
ceeding will  find  ample  justification  in  the  greater  ease 
with  which  we  shall  thus  be  enabled  to  understand  the 
more  complex  examples  which  we  must  afterwards 
examine. 

Taking  a  regularly  shaped  muscle,  in  which  the 
fibres  are  parallel,  we  will  cut  out  a  part  of  this  by 
making  two  even  cuts  at  right  angles  to  the  direction 
of  the  fibres.  A  piece  of  this  sort  may  be  called  a 
regular  viuscle-^rism.  It  is,  according  to  the  shape  of 
the  muscle  used,  either  circular  or  more  oval,  or  flat 
and  band-like ;  its  shape  makes  no  difference,  and  the 
length  and  diameter  are  of  equally  little  account.  The 
only  essential  point  is  that  all  the   muscle-fibres  ^e 


190     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

parallel  to  each  other,  and  that  the  two  cuts  are  made 
at  right  angles  to  the  direction  of  the  fibres.  Fig.  49 
diagrammatically  represents  a  regular  muscle-prism  of 
this  sort.  The  horizontal  stripes  represent  the  separate 
bundles  of  the  fibres.  The  outer  surface  of  the  prism, 
which  therefore  corresponds  with  the  upper  surface  of 
the  fibres,  is  called  the  longitudinal  section  of  the 
prism ;  and  the  terminal  surfaces,  at  right  angles  to 
the  longitudinal  section,  are  the  cross-sections  of  the 
muscle-prism.  The  lines  running  at  right  angles  to 
the  direction  of  the  fibres  are,  as  we  shall  presently 
find,  tension -curves. 

A  regular  muscle-prism  such  as  this  exhibits  a  very 


n/  u'  a/      a'       a'  a  ^'        a'     a    a  O- 

Fig  J9.    A  kegulau  miscle-puism. 

simple  distribution  of  tension.  All  the  lines  of  tension, 
or  the  iso-electric  curves,  run  on  the  surface  and  are 
parallel  to  the  cross-sections.  Eound  the  middle  of  the 
.  muscle-prism  passes  a  line  separating  it  into  two  sym- 
metrical halves;  this  we  will  call  the  equator.  The 
greatest  'positive  tension  to  be  found  anywhere  on  the 
surface  prevails  at  this  point.  Every  point  on  the 
equator  has  a  greater  positive  tension  than  any  other 
point  on  the  longitudinal,  or  the  cross-section.  On 
either  side  from  the  equator,  the  positive  tension  gra- 
dually decreases  along  the  longitudinal  section  quite 
regularly  in  both  directions,  until,  at  the  point  where 
the  longitudinal  meets  the  cross-section,  it  =  0. 
*  On    the    cross-sections    themselves   the    tension   is 


CURRENTS    AND    TENSION    IN    A    MUSCLE-PRISM.        191 

everywhere  negative,  and  the  greatest  negative  tension 
prevails  at  the  centre  of  these,  and  decreases  from  these 
points  up  to  where  the  cross-sections  meet  the  longitu- 
dinal section. 

2.  From  this  distribution  of  the  tensions  it  is  easy 
to  infer  the  phenomena  which  the  muscle  shows  when 
it  is  inserted  between  the  pads  of  the  diverting  vessels 
above  described,  or  between  the  diverting  cylinders 
which  represent  the  feet  of  the  diverting  arch.  It  is 
evident  that  no  current  will  result  when  two  points  on 
the  equator,  or  two  points  on  any  one  of  the  tension- 
curves  are  tested.  Nor  will  any  current  result  when 
two  different  points,  on  either  side  of  the  equator,  are 
connected,  if  these  points  are  equidistant  from  the 
equator.  Xor  will  any  current  result  when  the  two 
cross-sections  are  applied  to  the  pads ;  but,  on  the  con- 
trary, a  current  will  be  observed  as  soon  as  any  point 
on  the  longitudinal  section  and  any  one  on  either  of 
the  cross-sections  are  connected,  or  when  two  points 
on  the  longitudinal  section,  situated  at  unequal  dis- 
tances from  the  equator,  touch  the  pads ;  or,  finally, 
when  two  points  on  the  same  cross-section,  or  two 
points,  one  on  each  of  the  two  cross-sections,  situated 
at  unequal  distances  from  the  central  point,  are  con- 
nected. The  strongest  current  will  result  when  a  point 
on  the  equator  is  connected  with  the  central  point  on 
one  of  the  cross-sections ;  weaker  currents  are  gene- 
rated when  two  unsymmetrical  points  on  the  longi- 
tudinal section,  or  two  unsymmetrical  points  on  the 
cross-section  are  connected.  All  these  cases  are  re- 
presented in  fig.  50.  The  rectangular  figure  abed 
represents  a  section  through  the  muscle-prism;  a  b 
and   c  d  are  transverse  sections  throufjh  the  long-itu- 


192 


PHl'SIOLOGY    OF   MUSCLES   AND   NERVES. 


dinal  section,  and  a  c  and  b  d  are  transverse  sections 
through  the  cross-section.  The  curved  lines  represent 
the  diverting  arches,  and  the  arrows  show  the  direction 
of  the  currents  which  are  generated  in  these.  No 
currents  are  generated  in  arches  6,  7,  or  8,  for  these 
unite  symmetrical  points. 

Moreover,  the  rate  at  which  the  tension  decreases 
in  the  longitudinal  section  is,  not  regular,  but  at  a 
gi'adually  increasing  speed  from  the  equator  to  the 
ends.     If,  therefore,  we  find  these  iso-electric  curves,  the 


Fig.  50.    Currents  in  a  jirscLE-PRisM. 


tensions  of  which  differ  by  a  definite  amount,  these,  in 
the  centre  of  the  muscle-prism,  are  at  some  distance 
from  each  other,  but  gradually  approach  more  closely 
together  toward  the  edffe  of  the  cross-section.  If  the 
tension  prevailing  at  each  point  in  one  side  of  a  longi- 
tudinal section  is  represented  by  the  height  of  a  straight 
line  drawn  at  right  angles  to  that  side  of  the  longitu- 
dinal section,  then  the  curve  which  unites  the  heads  of 
these  Hues  is  level  at  the  centre  of  the  longitudinal 
section,  but  sinks  rapidly  down  toward  the  edges  of  the 
cross-section.     A  somewhat  sunilar  fact  is  observable  on 


THE   MUSCLE-RHOMBUS. 


193 


the  cross-sections,  where  the  tension-curves,  correspond- 
ing with  equal  differences  of  tension,  are  nearer  to- 
gether toward  the  edge  of  the  longitudinal  section 
than  in  the  middle.  If  the  feet  of  the  diverting  arch 
■are  equidistant,  the  currents,  both  from  the  longitu- 
dinal section  and  from  the  cross-sections,  are  therefore 
stronger  the  nearer  is  the  point  under  examination  to 
the  limit  between  the  longitudinal  and  cross-sections. 
Fig.  51  shows  this  circumstance:  A  in  the  figure  re- 
presents the  tensions  on  one  of  the  longitudinal  sections 


J'iG.  51.    Tension'  ox  the  longitudinal  and  ckoss  sections  of  a 

JILSCLE-PKISM. 

and  on  one  of  the  cross-sections  of  the  transverse  section 
represented  in  fig.  50 ;  while  at  B  the  tension-curves  in 
a  cross-section  itself  are  represented.  The  latter,  if  the 
muscle-prism  is  perfectly  round,  are  concentric  circles. 
In  order  to  judge  of  the  direction  and  strength  of  the 
current  resulting  when  a  conducting  arch  is  applied  to 
any  two  points  of  a  muscle-prism,  it  is  only  necessary 
to  determine  the  difference  of  tensions  at  the  feet  of 
the  arch,  and,  in  so  doing,  to  notice  that  when  positive 
tension  prevails  at  one  of  these  points,  negative  tension 
at  the  other,  the  current  tbrouofh  the  arch  is  always  in 


194  PHYSIOLOGY    OF    MUSCLES    AND   NERVES. 

the  direction  from  the  positive  to  the  negative  point ; 
but  that,  if  the  feet  are  both  positive,  or  both  negative, 
the  current  passes  from  the  more  to  the  less  positive 
point,  or  from  the  less  to  the  more  negative  point. 
From  the  curves  in  A  and  B,  fig.  51,  which  show  the. 
tensions,  the  currents  indicated  in  fig.  50  may  therefore 
easily  be  discovered. 

3.  Once  more  let  us  take  a  muscle,  the  fibres  of 
which  are  parallel,  and  cut  a  piece  out  of  this,  but  in 
such  a  way  that  the  cross-section,  instead  of  being  at 
right  angles  to  the  direction  of  the  fibres,  is  obliquely 
directed  toward  the  latter.  A  piece  of  this  sort  may  be 
called  a  onuscle-rhombus ;  if  the  cross-sections  are 
parallel  to  each  other,  it  is  a  regular  m,uscle-7'ho7)ihus  ; 
if  otherwise,  an  irregular  r)%uscle-rhombus.  In  such  a 
muscle-rhombus,  the  distribution  of  the  tensions,  and, 
consequently,  the  form  of  the  iso-electric  curves,  is 
much  more  complex  than  in  a  muscle-prism.  In  this 
case  the  cm'ves  are  not,  as  in  a  muscle-prism,  parallel, 
but  are  sometimes  of  very  complex  form. 

It  is  true  that  in  this  case  also  there  is  the  main 
distinction  between  the  longitudinal  section,  or  outer 
surface  of  the  muscle-rhombus,  and  the  cross-sections. 
The  former  are  always  positive,  the  latter  negative. 
But  both  in  the  longitudinal  and  cross-sections  a 
difference  is  noticeable  between  the  obtuse  and  the 
acute  angles.  The  positive  tension  is  greater  at  the 
obtuse  than  at  the  acute  angles  of  the  longitudinal 
section ;  and,  similarly,  the  negative  tension  is  greater 
at  the  acute  than  at  the  obtuse  augles  of  the  cross- 
sections.  Consequently,  a  peculiar  displacement  of  the 
tension-curves,  of  which  fig.  52  is  intended  as  a  re- 
presentation, takes  place  in  a  regular  muscle-rhombus. 


THE    MUSCLE  RHOMBUS. 


195 


Let  us  suppose  that  the  muscle  from  which  the  rhombus 
was  cut  was  cyhndricaL  The  two  cross -sections  will 
then  form  ellipses ;  in  the  case  of  a  regular  muscle- 
rhombus,  equal  ellipses.  A  section  through  the  longi- 
tudinal axes  of  both  these  ellipses  will  therefore  give 
an  asymmetrical  parallelogram  with  two  obtuse,  and 
two  acute  angles  (a  rhomboid).  Such  a  section  is  re- 
presented in  the  figure.  In  it,  a  6  and  c  d  correspond 
with  the  longitudinal  section,  a  c  and  h  d  the  cross- 
sections.  The  latter  are  identical  with  the  longfitudinal 
axis  of  the  actiial  cross-sections.     On  the  side  corre- 


sponding with  the  longitudinal  section,  the  greatest 
positive  tension  is  no  longer  found  in  the  middle,  but 
is  removed  toward  the  obtuse  angles,  at  e  and  e\  The 
tensions  fall  very  rapidly  from  here  toward  the  obtuse 
angle,  gradually  toward  the  acute  angle.  In  the  cross- 
sections  the  greatest  negative  tension  occurs  near  the 
acute  angles ;  and  the  fall  toward  the  acute  angles  is 
very  abrupt,  that  toward  the  obtuse  angles  is  gradual. 

The  iso-electric  curves  on  such  a  regular  muscle- 
rhombus  in  the  cross -sections  form  ellipses,  one  pole 
of  which  corresponds  with  a  focus  on  the  edge  of  the 


198 


PHYSIOLOGY   OF   MUSCLES   AND    KERVES. 


cross-section,  near  the  acute  angle.  In  the  longitudinal 
section  they  form  spiral  lines,  which  run  obliquely  round 
the  outer  surface  of  the  cylinder.  The  electromotive 
equator,  which  unites  the  points  at  which  the  greatest 
positive  tension  prevails,  forms  a  line  round  the  circum- 


FiG.  53.    The  curuexts  ix  a  regular  muscle-rhombus. 


ference,  which  separates  the  rhombus  into  two  equal 
halves. 

Supposing  that  a  plane  is  drawn  in  such  a  regular 
muscle-rhombus,  through  the  small  axis  of  the  elliptic 
cross-sections,  a  rectangular  figure  will  be  obtained. 
The  muscle-fibres  lying  in  such  a  section  are  all  cut 
in  a  similar  way,  and  their  condition  is  exactly  alike. 
Therefore  in  this  section  also  the  greatest  tension  on 


IRREGULAE   MUSCLE-RHOMBl.  197 

the  longitudinal,  as  on  the  cross-sections,  is  situated  in 
the  centre,  and  an  arrangement  of  the  tensions  exactly 
similar  to  that  in  a  muscle-prism  is  observable. 

From  what  has  been  said,  the  direction  and  strength 
of  the  currents  which  are  generated  on  the  intercon- 
nection of  any  points  in  a  muscle-prism  by  the  appli- 
cation of  an  arch  may  easily  be  inferred.  They  are 
represented  in  fig.  53.  The  direction  of  the  currents 
in  the  applied  arches  is  in  every  case  indicated  by 
arrows ;  where  there  are  no  arrows  the  arch  connects 
two  points  of  equal  tension,  so  that  there  is  no  current 
(e.g.  arches  4  and  9).  The  currents  all  pass  from  the 
obtuse  to  the  acute  angle,  through  the  applied  arches, 
except  in  the  fifth  and  tenth,  in  which  the  direction  is 
reversed. 

4.  The  phenomena  iu  irregular  muscle-rhombi  do 
not  diflfer  essentially  from  those  just  described,  but  the 
arrangement  of  the  tensions  is  asymmetrical.  Passing 
to  muscles  in  which  the  arrangement  of  the  fibres  is 
irregular,  it  is  apparent  that  each  cut  made  must  always 
meet  a  part  of  the  fibres  obliquely,  and  that,  therefore, 
the  matter  just  explained  must  always  be  borne  in  mind 
in  explanation  of  the  phenomena,  which  are  sometimes 
very  complex.  Not  to  enter  too  far  into  details,  we 
need  only  say  that  the  same  fundamental  principle 
asserts  itself  in  all  muscles ;  everj^where  the  longi- 
tudinal section,  as  distinguished  from  the  cross-section, 
is  positive ;  and  in  all  cases  there  is  a  point  or  line  in 
the  longitudinal  section  which  is  the  most  positive, 
and  a  point  in  the  cross-section  which  is  most  negative ; 
so  that,  if  an  arch  is  applied,  currents  pass  through  this 
from  the  longitudinal  to  the  cross-section,  weaker  cur- 
rents between  points  in  the  longitudinal  section,  and 


198  PHYSIOLOGY    OF   MUSCLES   AXD    NERViiS. 

between  points  in  the  cross-section  respectively.  The 
position  of  these  most  strongly  positive  and  most 
strongly  negative  points  depends  on  the  angles  which 
the  fibres  form  with  the  cross-sections,  and  may  be 
found  by  the  rules  given  in  the  last  paragraph  as  to  the 
influence  of  oblique  section. 

Of  all  the  many  muscles  of  the  animal  body  one 
claims  special  attention,  because,  for  purely  practical 
reasons,  it  is  most  frequently  used  in  physiological  ex- 
periments :  this  is  the  calf-muscle  (771.  gastrocnemius). 
It  is  easily  prepared,  even  without  severing  its  connec- 
tion with  its  nerve,  a  fact  which,  for  reasons  presently 
to  be  stated,  is  of  great  importance.  It  affords,  as  wc 
shall  see,  a  powerful  current ;  it  long  retains  its  capacity 
for  action ;  and,  in  short,  it  has  many  advantages  by 
which  we  were  induced,  when  studying  the  activity  of 
muscle  and  the  excitability  of  nerves,  to  make  use  of  it 
almost  exclusively.  As,  however,  the  structure  of  the 
muscle  is  very  complex,  the  nature  of  its  electric  action 
is  by  no  means  easily  understood.  We  must,  however, 
describe  at  least  its  main  outlines,  as  we  must  employ 
the  muscle  in  further  important  experiments. 

In  order  to  understand  this  action  we  jnust  pre- 
viously observe  that  it  is  not  absolutely  necessary  to 
cut  a  piece  out  of  a  muscle,  but  that  entire  muscles  are 
also  capable  of  affording  currents.  In  dealing  with  the 
muscle-prism  and  muscle-rhombus,  we  assumed  that 
the  pieces  were  cut  from  parallel-fibred  muscles.  The 
longitudinal  sections  of  these  pieces  retained  their 
covering  of  muscle-sheath  (^perimysium)  and,  in  fact, 
corresponded  with  the  natural  surface  of  the  muscle. 
The  cross-cuts  were,  however,  made  into  the  actual 
substance  of  the  muscle,  so  that  part  of  the  interior 


THE    CURRENT    OF    M.    GASTROCNEMIUS.  199 

■was  laid  bare.  Such,  cross-sections  may  be  termed 
artificial,  while  the  longitudinal  sections  of  these  prisms 
or  rhombi  may  be  called  natural.  Longitudinal  sections 
may  also  be  formed  artificially,  by  splitting  the  muscle 
in  the  direction  of  its  fibres ;  and  we  may  speak  of 
natinral  cross-sections,  by  which  we  understand  the 
natural  ends  of  the  muscle-fibres  while  still  closed  with 
the  tendonous  substance.  IS  ow  the  action  both  of  lonofi- 
tudinal  and  of  cross-sections  is  the  same  whether  they 
are  natural  or  artificial.^  It  is,  therefore,  always  pos- 
sible to  obtain  currents  from  an  uninjured  muscle 
exactly  as  from  artificially  prepared  muscle-prisms  and 
rhombi. 

5.  To  the  circvimstance  that  it  can,  while  still  un- 
injured, afford  powerful  currents,  is  due  the  special 
importance  of  the  gastrocnemius.  This  muscle  may 
in  all  essential  points  be  classed  among  the  penniform 
muscles ;  though  in  reality  it  is  thus  conditioned  only 
towards  its  upper  tendon,  the  part  toward  the  lower 
tendon  being  rather  of  the  character  of  a  semipenniform 
muscle.  In  order  to  understand  its  structure,  let  us 
imagine  two  tendonous  plates,  an  upper  and  a  lower, 
connected  by  muscle-fibres  stretched  obliquely  between 
them,  so  as  to  form  a  semipenniform  muscle.  Now  let 
us  suppose  the  upper  tendonous  plate  to  be  folded  in  the 
middle,  as  a  sheet  of  paper  might  be,  and  that  the  two 
folded  hahes  are  in  apposition.  "NVe  now  have  an 
upper  tendon  plate,  situated  within  the  muscle,  from 
which  muscle-fibres  pass  obliquely  in  both  directions ; 
the  lower  tendon  has,  however,  been  so  bent  by  the 
folding  of  the  upper  so  that  the  whole  muscle  is  shaped 
like  a  turnip  split  in  a  longitudinal  direction,  the  flat 
'   Except icns  to  tliis  rule  will  presently  be  mentioned. 


200 


PHYSIOLOGY    OF    MUSCLES    AXD    NERVES. 


surface  of  which  (turned  toward  the  bone  of  the  lower 
leg)is  formed  solelyof  muscle-fibres, exhibiting  a  delicate 
longitudinal  streak  as  the  only  indication  of  the  tendon 
buried  within  it ;  the  arched  dorsal  surface  is,  on  the 
contrary,  clothed,  as  regards  the  lower  two-thirds  of  its 
length,  with  tendonous  substance  which  passes  below 
into  the  so-called  tendo  Achillis. 

It  is  evident  that  such  a  muscle  has  naturally  an 
oblique  cross-section,  represented  by  this  tendonous 
covering,  and  a  longitudinal  section  which  includes  the 
whole  of  the  flat,  and  a  little  of  the  curved  portion. 
This  muscle  can,   therefore,  without  any  further  pre- 


FiG.  54.    The  currents  of  a  gastrocnemius. 

paration  afford  currents ;  for  ^hich  reason  it  may  be 
most  advantageously  used  in  a  large  number  of  experi- 
ments. 

Eegarding  once  more  the  structure  of  the  gastro- 
cnemius, as  it  has  just  been  described,  a  natural  longitu- 
dinal section  is  recognisable  in  the  whole  flat  part  and 
a  little  of  the  upper  portion  of  the  curved  surface ;  and 
a  natural  cross-section  is  to  be  recognised  in  the  greater 
and  lower  part  of  the  curved  upper  surface.  No  second 
cross-section  exists  in  this  muscle,  for  the  upper  tendon 
is  buried  within  the  muscle.  The  currents  which  the 
muscle  sends  through  an  arch  applied  so  as  to  connect 


THE  CURRENT  OF  M.  GASTROCNEMIUS.      201 

different  points  on  its  outer  surface  will  now  easily  be 
understood,  and  are  as  represented  in  fig.  54.  It  is 
most  especially  necessary  to  notice  that  a  strong  current 
must  be  generated  on  the  interconnection  of  the  upper 
with  the  lower  end  of  this  muscle,  and  that  the  current 
within  the  arch  is  directed  from  the  upper  to  the  lower 
end  of  the  muscle.  The  upper  end  must  be  strongly 
positive ;  for  it  represents  the  middle  of  the  longitu- 
dinal section.  The  lower  end  must  be  strongly  negative ; 
for  it  is  the  acute  angle  of  an  oblique  cross-section. 
There  are  very  few  points  so  alike  in  the  matter  of  ten- 
sion that  no  current  results  from  their  connection.  A 
case  of  this  kind  is,  however,  shown  in  the  fourth 
arch. 


10 


202     PHYSIOLOGY  OF  MUSCLES  AXD  NERVES. 


CHAPTEE  XII. 

].  Negative  variation  of  the  muscle-current;  2.  Living  muscle  is 
alone  electrically  active  ;  3.  rarelectronomy  ;  4.  Secondarj^  pul- 
sation and  secondary  tetanus;  5.  Glands  and  their  currents. 

1.  The  powerful  current  afforded  by  an  entire  tyi.  gas- 
trocnemius enables  us  to  answer  the  important  question 
as  to  the  character  of  electric  phenomena  during  con- 
traction. All  that  is  necessary  is  to  prepare  this  muscle, 
together  with  its  nerve,  and  to  insert  its  upper  and 
lower  ends  between  the  pads  of  the  diverting  vessel 
already  described,  and  then  to  place  the  nerve  on  two 
wires  so  that  it  can  be  irritated  by  inductive  currents ; 
it  must  then  become  evident  whether  the  activity  of 
the  muscle  has  any  influence  on  its  electric  action  or 
not. 

In  order  to  carry  out  the  experiment,  let  us  suppose 
the  muscle,  as  shown  in  fig.  55,  placed  between  the 
pads  of  a  diverting  vessel,  these  pads  being  brought 
somewhat  near  each  other,  so  that  the  contact  of  the 
muscle  with  the  pads  is  not  disturbed  by  the  con- 
traction of  the  former.  The  nerve,  which  has  been 
extracted  with  the  muscle,  is  laid  on  two  wires  which 
are  connected  with  the  secondary  spiral  of  the  inductive 
apparatus.  A  key,  inserted  between  the  nerve  and  the 
spiral,  regulates  the  inductive  currents  so  that  the  nerve 
is  not  excited.     When  all  is  arranged,  and  the  multi- 


NEGATIVE    VARIATION    OF   THE    MUSCLE-CURRENT.    203 

plier  has  assumed  a  fixed  deflection,  the  extent  of  which 
depends  on  the  strength  of  the  muscle-current,  the  key 
at  S  is  opened.  Inductive  currents  pass  through  the 
nerve,  and  the  muscle  contracts.  At  the  same  instant 
the  deflection  of  the  multiplier  is  observed  to  decrease. 
If  the  irritation  of  the  nerve  is  interrupted,  the  deflec- 
tion of  the  multiplier  again  increases ;  and  when  the 
irritation  is  again  commenced,  it  again  decreases,  and 
this  process  continues  as  long  as  the  muscle  continues' 
to  afford  powerful  contractions. 


Fig.  00.    The  miscle-curkent  during  contr.vgtiox. 

This  experiment,  therefore,  shows  that  the  current 
of  the  gastrocnemius  is  weakened  during  contraction. 
This  may  be  most  strikingly  shown  by  a  variation  of 
the  experiment  just  described.  After  the  muscle  has 
been  placed  in  position  and  a  deflection  of  the  multi- 
plier has  been  caused,  the  muscle- current  may  be  com- 
pensated, as  described  in  Chapter  X.  §  4.  Two  currents, 
equal  but  in  opposite  directions — the  current  of  the 
muscle  and  that  of  the  compensator — now,  therefore, 
pass  through  the  muscle  and  cancel  each  other.  As 
long  as  these  two  currents  are  equal,  no  deflection  can 
occur  in  the  multiplier.     When  the  nerve  is  then  irri- 


204  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

tated  and  the  muscle  contracts,  the  current  becomes 
weaker ;  the  current  afforded  by  the  compensator  thus 
gains  preponderance,  and  effects  a  deflection  which  is, 
of  course,  in  exactly  the  opposite  direction  to  that  which 
was  originally  effected  by  the  muscle. 

There  is  strong  reason  to  believe  that  this  alteration 
in  the  styength  of  the  muscle-current  really  depends  on 
the  activity  of  the  muscle  and  is  not  occasioned  by  any 
.  accidental  circumstances.  Any  form  of  irritant  may  be 
used  indifferently  to  effect  this  activity.  Chemical, 
thermical,  or  other  irritants  may  be  used  in  place  of 
electricity  to  irritate  the  nerve ;  or  the  experiment  may 
be  made  on  a  muscle  which  is  still  in  connection  with 
the  whole  nervous  system,  and  the  contraction  may 
be  effected  by  influences  acting  through  the  spinal 
marrow  and  the  brain.  But  the  result  is  always  the 
same.  Even  when  external  circumstances  entirely  pre- 
vent contraction,  the  irritated  muscle,  without  changing 
its  form,  exhibits  this  decrease  in  its  current  as  soon  as 
it  is  brought  into  the  condition  of  activity  by  irritation. 
If,  for  example,  care  is  taken  that  the  muscle  retains 
its  form  unaltered,  by  fastening  it  in  a  suitable  clamp, 
and  if  this  muscle  is  then  irritated  into  activity,  the 
current  decreases  in  exactly  the  same  way  as  when  the 
experiment  is  carried  out  as  before  described. 

It  is  an  especially  interesting  fact  that  this  same 
phenomenon  may  also  be  observed  in  the  muscles  of 
living  and  uninjured  men.  It  is  very  hard  to  prove 
that  the  electric  action  of  muscles  of  living  animals 
in  their  natural  position  is  exactly  the  same  as  that  of 
muscles  when  extracted ;  but  the  fact  that  on  contrac- 
tion exactly  the  same  electric  processes  occur  in  muscles 
whether  they  are  in  their  natural  position  or  have  been 


NEGATIVE   VARIATION    OF   THE   MUSCLE-CX'KRENT.    205 

extracted  is  quite  certain.  E.  du  Bois-Eeymond  showed 
this  in  the  human  subject  in  the  following  Avay.  The 
ends  of  the  wire  of  the  multiplier  are  connected  with 
two  vessels  filled  with  liquid,  and  the  index  finger  of 
both   hands  is   chpped  in  these  vessels,  as  in  fig.  56. 


Fig.  56.     Dkflectiox  ov  the  magnetic  needle  by  the  avii.l. 

A  rod  arranged  in  front  of  the  vessel  serves  to  steady 
the  position  of  the  hands.  Currents  are  then  present 
in  the  muscles  of  both  arms  and  of  the  breast,  which, 
since  the  groups  of  muscles  ai'e  symmetrically  arranged, 
cancel  each  other,  acting  one  on  the  other.  If  for  any 
reason  any  current  remains  uncancelled,  it  may  be 
compensated  in  the  way  before  described.  When  all 
is  thus  arranged,  and  the  man  strongly  contracts  the 


206      PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

muscle  of  one  arm,  the  result  is  an  immediate  deflec- 
tion of  the  multiplier,  which  indicates  the  presence  of 
a  current  ascending  in  the  contracted  arm  from  the 
hand  to  the  shoulder.  If  the  muscles  of  the  other  arm 
are  contracted,  a  deflection  occurs  in  the  opposite  direc- 
tion. We  are,  therefore,  able  by  the  mere  power  of  the 
will  to  generate  an  electric  current  and  to  set  the  mag- 
netic needle  in  motion. 

Summing  up  all  that  has  been  said,  it  appears  that, 
during  muscular  contraction,  the  electric  forces  acting 
in  the  muscle  undergo  a  change  which  is  independent 
of  the  alteration  of  form  in  the  muscle,  and  is  con- 
nected with  the  fact  of  activity  itself.  As,  dm'ing  this 
alteration,  the  current  which  may  be  exhibited  in  an 
applied  arch  becomes  weaker,  the  term  negative-varia- 
tion of  the  muscle-current  has  been  applied  to  it. 

2.  The  negative  variation  of  the  muscle-current  on 
contraction,  as  described  in  the  last  paragraph,  is  a 
proof  of  the  fact  that  in  the  electric  action  of  muscle 
we  have  to  do,  not  with  an  accidental  physical  pheno- 
menon, but  with  an  action  very  closely  connected  with 
the  essential  physiological  activities  of  muscle.  It  is 
therefore  worth  while  to  trace  an  action  of  this  sort 
more  accurately,  as  it  may  possibly  aid  in  the  explana- 
tion of  the  activity  of  the  muscle. 

It  may,  in  the  first  place,  be  safely  asserted  that  all 
muscles  of  all  animals,  as  far  as  they  have  at  present 
been  examined,  exhibit  the  same  electric  action.  Even 
smooth  muscles  act  electrically  in  the  same  way; 
though  in  that  case  the  phenomena  are  less  regular, 
owing  to  the  fact  that  the  fibres  are  not  so  regularly 
arranged  as  in  striated  muscle.  Moreover,  the  electric 
activity  of  smooth  muscles  seems  to  be  somewhat 
weaker.     . 


LIVING    MUSCLE    ALOXE   ELECTRICALLY   ACTIVE.      207 

Further,  it  is  to  be  observed  that  the  electric  activity 
of  muscles  is  connected  with  their  physiological  power 
of  accomplishing  work.  When  muscles  die,  the  electric 
phenomena  also  become  weaker,  and  finally  cease  en- 
tirely when  death-stiffness  intervenes.  Muscles  which 
can  no  longer  be  induced  to  contract  even  by  very 
strong  irritants  may  indeed  still  show  traces  of  electric 
action  ;  but  this  power  soon  disappears.  Nor  does  the 
electric  activity,  when  it  has  once  disappeared  from  a 
rigid  and  dead  muscle,  ever,  under  any  circumstances, 
return. 

Although  it  may  be  assumed  as  proved  that  the 
electric  activity  of  muscle  is  connected  with  the  living 
condition  of  the  muscular  tissue,  it  must  not,  however, 
be  inferred  from  this  that  this  activity  is  necessarily 
always  present  during  life.  It  is  conceivable  that  the 
preparation  necessary  for  the  study  of  electric  action 
(the  exposure  of  the  muscle,  its  connection  with  the 
arch,  &c.)  might  produce  changes  in  the  living  muscle 
Avhich  are  themselves  the  cause  of  electric  activity. 
To  satisfy  this  doubt  it  would  be  necessary  to  show  the 
previous  existence  of  electric  activity,  wherever  it  is 
possible,  in  uninjured  men  and  animals.  The  great 
difficulty  which  lies  in  the  way  of  such  proof  has  already 
been  mentioned.  The  more  complex  is  the  arrange- 
ment of  the  fibres  and  the  position  of  the  separate 
muscles  present  in  any  part  of  the  body,  the  harder  is  it 
to  say,  a  priori,  how  the  separate  cm-rents  of  the  various 
muscles  combine.  It  must  also  be  added,  that  the  skin, 
through  which  the  electric  action  is  necessarily  observed, 
is  in  itself  somewhat  electrically  active,'  and  that,  in 
other  ways  also,  it  increases  the  difficulty  of  proving  the 
'  Tliesj  skin-currents  will  be  again  mentioned. 


208  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

presence  of  muscle-currents.  Due  regard  being  had 
to  all  these  circumstances,  the  conclusion  may  yet  be 
drawn  that  entirely  uninjured  muscles  situated  in  their 
natiu'al  position  are  in  themselves  electrically  active. 
It  is  true  that  this  has  been  repeatedly  denied  by  many 
observers.  Our  reason  for  reasserting  it  is  that  the  ex- 
planation of  the  phenomena  on  the  assumption  of  the 
absence  of  electromotive  opposition  in  uninjm-ed  muscle 
necessitates  very  forced  and  complicated  assumptions, 
while  our  view  is  able  to  explain  all  the  known  facts 
very  simply  and  in  a  thoroughly  satisfactory  manner. 

3.  The  electric  action  of  muscles  which,  though  ex- 
tracted, are  otherwise  uninjm'ed,  is  often  very  weak, 
and  is  sometimes  even  reversed  ;  that  is  to  say,  the 
natural  cross-section  is  not  negative,  but  positive,  in 
opposition  to  the  longitudinal  section.  This  condition 
is  found  chiefly  in  the  muscles  of  frogs  which  have 
been  exposed  during  life  to  severe  cold.  It  is,  however, 
only  necessary  to  remove,  in  any  way,  the  natural  cross- 
section  with  its  tendonous  covering,  in  order  to  elicit 
action  of  normal  character  and  strength.  In  parallel- 
fibred  muscles  it  is  often  necessary  to  remove  a  short 
piece,  of  from  1  to  2  mm.  in  length,  from  the  end 
of  the  muscle-fibres,  before  meeting  with  an  artificial 
cross-section  in  which  the  action  is  powerful. 

This  phenomenon,  which  was  called  parelectronomy 
by  E.  du  Bois-Eeymond,  because  it  differs  from  the 
usual  electric  action  of  muscles,  gave  rise  to  that  ex- 
planation of  the  electric  phenomena  according  to  which 
the  electric  opposition  between  different  portions  of  the 
muscle  is  not  present  in  the  normal  muscle,  but  only 
intervenes  on  the  exposure  of  the  miiscle.  The  diffi- 
culty mentioned  above,  of  showing  the  muscle-currents 


SECONDARY  PULSATION  AND  TETANUS.      209 

in  uninjured  animals,  lent  force  to  this  explanation. 
Yet  no  sufficiently  strong  proof  of  this  view  has  been 
brought  forward  to  cause  us  to  doubt  the  existence  of 
electric  action  in  uninjui'ed  and  living  muscles. 

The  question  does  not,  however,  essentially  affect 
the  physiological  conception  of  the  relation  of  this  ac- 
tivity to  the  other  vital  qualities.  It  is  unimportant 
whether  the  separate  portions  of  the  outer  surface  of 
a  muscle  are  similar  or  dissimilar  in  the  matter  of  ten- 
sion. The  only  essential  point  is,  as  to  whether  electro- 
motive forces  are  present  within  the  muscle,  and  whether 
these  are  in  any  way  related  to  the  physiological  work 
of  the  muscle.  Negative  variation  has  a  deeply  impor- 
tant bearing  on  this  question,  so  that  we  will,  after  this 
digression,  return  to  a  more  detailed  study  of  this 
phenomenon. 

4.  It  is  unnecessary  to  tetanise  the  muscle  in  order 
to  exhibit  negative  variation.  If  a  sufficiently  sensitive 
multiplier  is  used,  a  single  pulsation  suffices.  Even 
without  a  multiplier,  negative  variation  may  be  very 
well  shown  in  the  following  way. 

On  a  gastrocnemius  prepared  with  its  nerve  (fig.  57), 
or  on  an  entire  thigh  (J5,  fig.  58),  the  nerve  of  a  second 
gastrocnemius,  or  thigh.  A,  is  placed  in  such  a  way 
that  one  part  of  the  nerve  touches  the  tendon,  another 
part  touches  the  surface  of  the  muscle-fibres.  The  nerve 
then  represents  a  sort  of  applied  arch,  uniting  the  nega- 
tive cross- section  and  the  positive  longitudinal  section, 
and  a  current,  corresponding  with  the  difference  of  ten- 
sion at  these  points  of  contact,  passes  through  the  nerve.' 

'  This  current  may  at  the  moment  of  its  generation,  i.e.  on  tlie 
sudden  application  of  the  nerve,  exercise  an  irritating  effect  on 
the  nerve  and  may  elicit  a  pulsation  of   the  muscle.     This  is  the 


210 


PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 


If  the  nerve  of  the  muscle  B  is  then  irritated,  either  by 
closing  or  by  opening  a  current,  by  an  inductive  shock,  by 
scission,  by  pressure,  or  in  any  other  way,  the  muscle  A 
is  observed  to  pulsate  also.  This  is  called  second- 
ary 'pulsation.  The  explanation  is  easy.  The  muscle- 
current  from  B  dairing  its  pulsation  suffered  a  negative 
variation.  This  variation  took  place  also  in  that  por- 
tion of  the  current  which  passed  through  the  applied 
nerve  ;  and,  as  every  nerve  is  irritated  by  sudden  change 


Fig.  57  &  58.     SEcoNDARr  pulsation. 

in  the  strength  of  the  current,  the  result  was  a  secon- 
dary pulsation. 

A  variation  of  this  experiment  is  very  interesting. 
The  heart  of  a  frog  continues  to  beat  for  some  time 
after  it  has  been  extracted  from  the  body.  If  the  nerve 
of  a  muscle  is  placed  on  this  heart  so  as  to  touch  its 
base  and  point,  the  muscle  pulsates  at  every  beat  of 
the  heart.  In  this  case,  the  heart-muscle  affords  the 
muscle-current,  the  negative  variation  of  which  irritates 
the  applied  nerve  and  causes  secondary  pulsation. 

'pulsation   without    metals'    {Zuchnni  oluie    Mctallc')    which    has 
gained  celebrity  from  the  wa-itings  of  Volta,  Humboldt,  and  others- 


SECONDARY  PULSATION  AND  TETANUS.      211 

If  the  nerve  of  one  muscle  is  placed  on  a  second 
muscle  in  such  a  way  that  no  observable  part  of  the 
current  passes  through  the  former  (as  shown  in  the 
nerve  of  the  muscle  C,  in  fig.  58),  no  secondary  pul- 
sation takes  place  in  the  muscle. 

If  the  nerve  of  the  first  muscle  is  repeatedly  irri- 
tated in  such  a  way  that  the  muscle  B  passes  into  a 
state  of  tetanus,  then  the  muscle  A  assumes  the  con- 
dition of  secondary  tetanus.  This  important  experi- 
ment shows  that  variations  of  electric  activity  take 
place  in  rapid  succession  in  tetanised  muscle.  For  it 
is  only  owing  to  such  rapidly  succeeding  variations  in 
the  strength  of  the  current  that  a  persistent,  tetanising 
irritation  can  occur  in  the  second  nerve.  Just  as  the 
phenomenon  of  muscular  tone  led  us  to  the  conclusion 
that  muscle-tetanus,  though  the  similarity  in  external 
form  is  apparently  complete,  is  not  a  state  of  rest,  but 
that  the  molecules  of  the  muscle  must  be  in  constant 
internal  motion  during  tetanus,  so  we  now  find  from 
the  phenomenon  of  secondary  tetanus  that  throughout 
its  duration  a  continual  variation  occurs  in  its  elec- 
tric condition  ;  and  from  this  we  may  infer  that  elec- 
tric variation  is  connected  with  the  motion  of  the 
molecules  which  causes  contraction. 

More  detailed  study  of  negative  variation  has  also 
shown  that  it  occurs  even  in  the  stage  of  latent  irri- 
tation, that  is,  at  a  time  at  which  the  muscle  has  not 
yet  altered  its  external  form  in  any  way.  It  has  also 
been  found  that  the  electric  change  which  occurs  on 
irritation  propagates  itself  when  the  muscle-fibre  is 
partially  irritated  at  a  rate  equal  to  that  of  the  propa- 
gation of  the  contraction  (from  3  to  4  m.  per  second : 
cf.  ch.  vi.  §  5,  p.   100).     When,  therefore,  a  muscle- 


212  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

fibre  of  some  length  is  irritated  at  one  point,  an  electric 
change  at  first  occurs  only  at  this  point ;  this  continues 
an  extremely  brief  time,  and  then  runs  wave-like  along 
the  muscle-fibre ;  and  this  electric  change  is  then  fol- 
lowed by  the  mechanical  change  of  contraction  and 
thickening,  which  is  called  contraction,  and  which  then 
propagates  itself  in  a  similar  wave-like  manner.  If, 
however,  the  whole  fibre  is  irritated  at  once,  the  elec- 
tric change  occurs  simultaneously  throughout  the  fibre, 
and  this  is  then  followed  by  the  mechanical  change. 

5.  The  glands  are  in  many  points  very  similar  to 
the  muscles,  though  their  structure  is  so  different.  A 
gland  of  the  simplest  form  is  a  cavity  lined  with  cells, 
opening  by  a  longer  or  shorter  passage  through  the 
outer  surface  of  the  mucous  membrane,  or  the  outer  skin 
{coriiini),  which  lies  above  it.  The  cavity  may  be  hemi- 
spherical, flask-shaped,  or  tubular.  In  the  latter  case  the 
tube  is  often  very  long,  and  is  either  wound  Hke  a  thread, 
or  is  coiled,  and  is  sometimes  expanded  at  its  closed 
end  in  the  form  of  a  knob.  These  are  all  sUnple  glands. 
Compound  glands  are  found  when  several  tubular  or 
knob-shaped  glands  open  with  a  common  mouth.  Sub- 
stances, often  of  a  very  peculiar  character,  are  found 
within  the  glands,  and  are  secreted  on  to  the  outer 
surface  through  the  mouth.  These  are  the  sweat  and 
fat  of  the  skin,  which  are  prepared  in  the  sweat  or  fat 
glands  of  the  skin,  the  saliva  and  the  gastric  juice, 
which,  owing  to  their  power  of  fermentation,  play  an 
important  part  in  digestion,  the  gall,  which  is  formed 
within  the  liver,  and  other  substances.  The  similarity 
alluded  to  between  the  muscles  and  the  glands  consists 
in  the  dependence  of  both  on  the  nerves.  If  a  nerve 
which  is  connected  with  a  muscle  is  irritated,  the  muscle 


GLANDS  AND  TDEIR  CURRENTS.         213 

becomes  active,  that  is,  it  contracts;  and  if  a  nerve  which 
is  connected  with  a  gland  is  irritated,  the  gland  be- 
comes active,  that  is,  it  secretes.  If,  for  example,  the 
nerves  which  pass  into  a  salivary  gland  are  irritated,  the 
saliva  may  be  made  to  ooze  in  a  stream  from  the  mouth 
of  the  gland.  It  is  certainly  an  important  fact  that, 
except  muscles  (and  disregarding  the  nerves,  which  will 
be  spoken  of  in  the  following  chapter),  the  glands  are 
the  only  tissue  which  has  been  shown  to  possess  regular 
electric  activity.  Tliis  is  not,  indeed,  true  of  all  glands, 
but  only  of  the  simple  forms,  the  bottle-shaped  or  skin 
glands.  Wherever  a  large  number  of  these  occur  regu- 
larly arranged,  side  by  side,  it  is  foimd  that  the  lower 
surface,  that  which  forms  the  base  of  the  gland,  is  posi- 
tively electric,  while  the  upper  surface,  that  which  forms 
the  exit  duct  of  the  gland,  is  negatively  electric.  This  is 
best  shown  in  the  skin  of  the  naked  amphibia,  in  which 
glands  abound,  and  in  the  mucous  membrane  of  the 
mouth,  stomach,  and  intestinal  canal  of  all  animals. 
In  these  tissues  all  the  glands  are  arranged  in  the  same 
order,  side  by  side,  and  all  act  electrically  in  the  same 
direction.^  In  compound  glands,  on  the  contrary,  the 
separate  gland  elements  are  arranged  in  all  possible  di- 
rections, so  that  the  actions  are  irregular  and  cannot  be 
calculated. 

In  the  skin-glands  of  the  frog,  as  in  the  glands  of 

'  These  currents  of  tlie  skin-glands  afford  one  of  the  reasons  to 
which  allusion  has  already  been  made  (§  2)  why  the  indication  of 
muscle-currenls  in  living  and  uninjured  animals  is  beset  with  diffi- 
culties. As  the  currents  of  the  skin-glands  at  two  points  of  the 
skin  from  which  the  muscle-current  is  to  be  diverted  are  not 
always  of  equal  strength,  therefore  the  action  of  the  skin  mingles 
with,  and  affects  that  of  the  underlying  muscles,  so  as  to  hinder  the 
detection  of  the  latter. 


214     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

the  mucous  membrane  of  the  stomach  and  intestinal 
canal,  it  may  be  clearly  shown  that  the  electric  force 
is  really  situated  in  the  glands.  On  irritation  of  the 
nerves  which  pass  into  the  skin  by  which  the  glands 
are  excited  into  activity,  the  gland-current  decreases  in 
strength,  and  exhibits  a  negative  variation,  just  as  the 
muscle-current  decreases  when  the  muscle  is  excited 
into  activity.  In  this  case,  also,  a  relation  therefore 
exists  between  the  activity  and  the  electric  condition ; 
and  this  adds  to  the  similarity  between  muscles  and 
glands. 

Engelmann  tried  to  explain  the  secretion  of  the 
glands  physically,  by  the  electric  cmTcnts  present 
within  them.  This  must,  however,  be  regarded  as  not 
yet  sufficiently  confirmed  to  claim  further  attention  iu 
this  place. 


CHAPTEE    XIII. 

1.  The  nerve-current ;  2.  Negative  variation  of  the  nerve-current ; 
3.  Duplex  transmission  in  the  nerve ;  4.  Rate  of  propagation 
of  negative  variation;  5.  Electrotonus ;  6.  Electric  tissue  of 
electric  fishes  ;  7.  Electric  action  in  plants. 

1.  In  addition  to  the  many  points  of  similarity 
between  muscles  and  nerves  exhibited  in  their  be- 
haviour when  irritated,  it  cannot  escape  notice  that 
the  nerves  also  exhibit  electric  phenomena,  and  that 
they  do  this  in  exactly  the  same  way  as  does  muscle. 
Nerves  being  formed  of  separate  parallel  iibres,  these 
phenomena  are  exactly  analogous  to  those  in  a  regular 
muscle-prism;  only  that  in  a  cross-section  of  a  nerve, 
on  account  of  its  small  extent,  diftereuces  of  tension 
cannot  be  shown  at  the  various  points,  and  the  cross- 
section  must  be  regarded  as  a  single  point. 

In  an  extracted  piece  of  nerve  all  the  points  on 
the  upper  surface,  that  is,  on  the  longitudinal  section, 
are  as  a  fact  positive,  in  distinction  from  those  on  the 
cross-section,  which  are  all  of  one  kind.  On  the  lonffi- 
tudinal  section  the  greatest  positive  tension  is  always 
in  the  centre,  and  the  tension  decreases  toward  the 
cross-sections,  just  as  in  the  muscle-prism,  at  first 
slowly,  afterwards  more  abruptly,  as  shown  in  fig.  59. 

Because  of  the  small  diameter  of  the  nerve-trunks, 
distinction  cannot,  of  course,  be  drawn  between  straight 


216     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

and  oblique  cross-sections,  sucli  as  we  made  in  the  case 
of  muscle ;  nor  can  phenomena  due  to  the  oblique  course 
of  the  fibres  be  detected,  as  in  muscle.  Where  larger 
masses  of  nerve-substance  occur,  as  in  the  dorsal  mar- 
row and  brain,  the  course  of  the  fibres  is  so  complex 
that  nothing  can  be  affirmed  except  that  the  cross- 
sections  are  always  negative  in  distinction  from  the 
natural  upper  surface  or  longitudinal  section. 

2.  If  a  current  is  conducted  from  any  two  points  on 
the  longitudinal  section  of  a  nerve,  or  from  one  point 
on  the  longitudinal  section  or  one  on  the  cross-section, 
and  if  the  nerve  is  then  irritated,  the  nerve-current 
evidently  becomes  weaker.  It  does  not  matter  what 
form  of  irritation  is  used,  provided  that  it  is  sufficiently 
strong  to  cause  powerful  action  in  the  nerve.  It  thus 
appears  that  in  the  nerve,  as  in  the  muscle,  a  change 
in  the  electric  condition  is  connected  with  its  activity, 
and  that  this  change  is  a  decrease,  or  negative  variation 
of  the  nerve-current.  We  must  now  go  back  to  the 
statement  already  made  (chap.  vii.  §  2),  that  the  ac- 
tive condition  of  the  nerve  is  not  shown  by  any  change 
in  the  nerve  itself.  We  then  found  it  necessary,  in 
order  to  observe  the  action  of  the  nerve,  to  leave  it  in 
undisturbed  connection  with  its  muscle.  The  muscle 
was  used  as  a  reagent,  as  it  were,  for  the  nerve,  because 
in  the  latter  neither  optical,  chemical,  nor  any  other  in- 
dicable  changes  could  be  observed.  In  its  electric  quali- 
ties we  have,  however,  now  found  a  means  of  testing 
the  condition  of  the  nerve  itself.  Whatever  view  is 
taken  as  to  the  causes  of  electric  action  in  nerves,  it 
is  at  least  certain  that  every  change  in  the  electric  con- 
dition must  be  founded  on  a  change  in  the  natm*e  or 
arrangement  of  the  nerve  substance ;  and  that  there- 


DUPLEX    TRAXSiSnSSIOX   IN   THE   NERVE. 


217 


fore  the  evident  negative  variation  of  the  nerve-current 
is  a  sign —  as  yet  the  onl}^  known  sign — of  the  processes 
which  occur  within  the  nerve  during  activity.  This  sign, 
therefore,  affords  an  opportunity  of  studying  the  ac- 
tivity of  the  nerve  itself  independently  of  the  muscle. 
3.  E.  du  Bois-Reymond  made  an  important  use  of 
this  fact  in  order  to  determine  the  significant  question, 
whether  the  excitement  in  the  nerve-fibre  is  propagated 
only  in  one,  or  in  both  directions.  If  an  uninjured 
nerve  trunk  is  irritated  at  any  point  in  its  course,  two 


TliXSlOX    IN  MiltVES. 


actions  are  usually  observable ;  the  muscles  connected 
with  the  nerve  pulsate,  and,  at  the  same  time,  pain  is 
caused.  The  excitement  has  therefore  been  transmitted 
from  the  irritated  point  both  to  the  periphery  and  to 
the  centre,  and  it  exercises  an  influence  in  both  places. 
Now,  it  may  be  shown  that  in  such  cases  two  differ- 
ent kinds  of  nerves  are  present  in  the  nerve- trunk 
— motor  nerves,  the  irritation  of  which  acts  on  the 
muscle ;  and  sensory  nerves,  the  irritation  of  which 
causes  pain.  In  some  places  each  of  these  kinds  of 
fibre  occurs  separately;  and  where  this  is  the  case,  irri- 
tation of  the  one  results  only  in  motion,  irritation  of 
the  other  only  in  sensation.  It  is  evident,  therefore, 
that  the  experiment  in  no  way  determines  whether  when 
a  motor  nerve  alone  is  irritated,  the  excitement  is  trans- 


218  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

mitted  only  toward  the  periphery  or  also  toward  the 
centre ;  or  as  to  whether,  when  a  sensory  nerve  alone  is 
irritated,  the  excitement  is  transmitted  only  toward  the 
centre  or  also  toward  the  periphery.  For  as  the  sensory 
nerves  do  not  pass  at  the  periphery  into  muscles,  by 
means  of  which  their  actions  could  be  expressed,  there 
is  no  means  of  telling  whether  the  excitement  in  them 
is  transmitted  to  the  periphery.  But  our  knowledge  of 
the  electric  changes  which  occur  during  activity  affords 
a  means  of  determining  this  question.  For  these 
changes  are  observable  in  the  nerve  itself,  independently 
of  the  muscles  and  other  terminal  apparatus.  If  a 
purely  motor  nerve  is  irritated,  and  is  then  tested  at  a 
central  point,  negative  variation  is  found  to  occur  in 
this  also;  and  similarly,  if  a  purely  sensory  nerve  is 
irritated,  negative  variation  may  be  shown  in  a  part  of 
the  nerve  lying  between  the  irritated  point  and  the 
periphery.  This,  therefore,  shows  that  the  excitement 
in  all  nerve-fibres  is  capable  of  propagation  in  both 
directions ;  and  that  if  action  occurs  only  at  one  end, 
this  is  due  to  the  fact  that  a  terminal  apparatus  capable 
of  expressing  the  action  is  present  only  at  that  end.^ 

4.  If  negative  variation  in  the  nerve  current  is 
really  a  necessary  and  inseparable  sign  of  that  condition 
within  the  nerves  which  is  called  the  '  activity  of  the 
nerves,'  it  must,  like  the  excitement,  propagate  itself 
within  the  nerve  at  a  measurable  speed.  Bernstein 
succeeded  in  proving  this,  and  measured  the  speed  at 
which  the  propagation  occurs.  If  one  end  of  a  long 
nerve  is  irritated,  the  other  end  being  connected  with 
a  multiplier,  a  certain  time  must  elapse  before  the 
irritation,  and  consequently  also  the  negative  variation, 
*  See  Notes  and  Additions,  No.  11. 


RATE  OF  PROPAGATION  OF  NEGATIVE  VARIATION.    219 

reaches  the  latter  end.     In  ordinary  experiments  the 
irritation  oecnrs  continuously,  and  the  connection  of 
the  other  end  of  the  nerve  with  the  multiplier  is  also 
continuous.     But  the  time  which  elapses  between  the 
commencement  of  imtation  and  the  commencement  of 
nep^ative  variation  is,  even  in  the  case  of  the  longest 
nerves  with  which  experiments  can  be  tried,  far  too  short 
to  allow  of  observation  of  this  retardation.     Bernstein 
proceeded  as  follows  :  two  projecting  wires  were  fastened 
to  a  wheel  which  turned  at  a  constant  speed.     One  of 
these  wires,  at  each  revolution,  closed  an  electric  current 
for  a  very  brief  time,  and  at  regular  intervals  of  time 
repeatedly   effected  the  irritation  of  one  end    of  the 
nerve.     The  second  wire,  on  the  other  hand,  for  a  very 
brief  time  connected  the  other  end  of  the  nerve  with  a 
multiplier.     When  irritation  and  connection  with  the 
multiplier  occurred  simultaneously,  no  trace  of  negative 
variation  was  observable;  for,  before  the  latter  could  pass 
from  the  irritated  point  to  the  other  end  of  the  nerve,  the 
connection  of  the  latter  with  the  multiplier  was  again 
interrupted.     By  altering  the  position  of  the  wires  it 
was,  however,  possible  to  cause  the  connection  of  the 
nerve  with  the  multiplier  to  occur  somewhat  later  than 
the  irritation.     When  this  difference  in  time  reached  a 
certain  amount,  negative  variation  intervened.     Yroxn 
the  amount  of  this  time,  together  with  the  length  of  the 
passage  between  the  point  irritated  and  that  at  which 
the  current  is  diverted,  it  is  evidently  possible  to  calcu- 
late the  rate  of  propagation  of  the  negative  variation 
within  the  nerve.     Bernstein  in  this  way  determined 
the  rate  at  25  m.  per  second.     This  value  corresponds 
as  nearly  with  that  found  for  the  propagation  of  the 
excitement  in  the  nerves  (24-8  m. ;  see  ch.  vii.  §  3)  as 


220 


PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 


can  be  expected  in  experiments  of  this  nature ;  and  it 
may  be  unconditionally  inferred  from  this  correspond- 
ence that  negative  variation  and  excitement  in  the  nerves 
are  two  intimately  connected  and  inseparable  processes, 
or  rather  two  aspects  of  the  same  process  observed  by 
different  means. ^ 

5.  The  negative  variation  of  the  nerve  current  is 
not  the  only  electric  change  known  to  occur  in  nerves. 
Under  the  name  '  Electrotonus '  we  have  already  (ch. 
viii.  §  1,  p.  125)  mentioned  certain  changes  in  the  ex- 
citability which  occur  in  the  nerve  iibre  as  soon  as  an 


Fig.  60.    The  changes  in  tension  during  electeotonus. 

electric  current  is  transmitted  through  a  part  of  it. 
These  changes  in  the  excitability  correspond  with 
changes  in  the  electric  condition  of  nerves,  which  we 
called  electrotonic.  In  fig.  60,  71  u' represents  a  nerve, 
a  and  k  two  wires  applied  to  the  nerve  through  which  an 
electric  current  is  transmitted  from  a  toward  k;  a  is 
therefore  the  anode,  k  the  kathode  of  the  current  em- 
ployed for  the  generation  of  electrotonus.  As  soon  as 
this  current  is  closed,  all  the  points  of  the  nerve  on  the 
side  of  the  anode  (from  n  to  a)  became  inore  positive, 
all  on  the  side  of  the  kathode  (from  k  to  n)  more 

'  See  Notes  and  Additions,  No.  12. 


ELECTROTONUS.  221 

negative  than  they  were.  These  changes  are  not,  how- 
ever, the  same  in  degree  at  all  points ;  the  change  is 
greatest  in  the  immediate  neighbourhood  of  the  elec- 
trode, and  decreases  proportionately  with  the  distance 
from  this.  If  the  degree  of  positive  increase  from  a 
to  n  is  indicated  by  lines,  the  height  of  which  expi'esses 
the  increase,  and  if  the  tops  of  these  lines  are  con- 
nected, the  result  is  the  curve  n  p,  the  form  of  which 
shows  the  changes  in  tension  occurring  at  each  point. 
The  changes  on  the  kathode  side  may  be  represented 
in  the  same  way,  but  that  in  this  case,  in  order  to 
show  that  the  tension  on  that  side  becomes  more  nega- 
tive, the  lines  may  be  drawn  downward  from  the  nerve. 
The  curved  line  q  n',  is  the  result.  The  two  portions 
of  the  curve  ii  p  and  q  n'  then  show  the  condition  of 
the  extrapolar  parts  of  the  nerve.  Nothing  is  really 
known  of  the  condition  of  the  intrapolar  portion  of  the 
nerve,  for,  for  external  technical  reasons,  it  is  im- 
possible to  examine  this.*  We  can  only  suppose  that 
changes  in  tension  such  as  those  indicated  by  the 
dotted  curve  p  q  occur  there. 

If  the  curve  in  fig.  60  is  compared  with  the  dia- 
gram of  the  changes  in  excitability  during  electro- 
tonus  (as  given  in  fig.  31,  page  130),  the  analogy 
between  the  two  phenomena  is  very  striking.  The 
two  really  represent  but  different  aspects  of  the  same 
process — of  the  changes,  that  is,  which  are  induced  in 
the  nerve  by  a  constant  electric  current.  Comparison 
of  the  two  curves  shows,  however,  that  when  the 
tension  becomes  more  positive  the  excitability  is  de- 
creased, and  that  Avhen  the  tension  becomes  more 
negative  the  excitability  is  increased.  Tlie  change 
'  See  Notes  and  Additions,  No.  13. 


222  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

in  tension  and  the  change  in  excitability  both  probably 
depend  on  molecular  changes  within  the  nerve,  as  to 
the  nature  of  which  we  are  not  yet  in  a  position  to  say 
anything  further,  but  the  simultaneous  appearance  of 
which,  under  the  influence  of  externally  applied  electric 
currents,  is  nevertheless  very  interesting  and  will  per- 
haps in  future  afford  a  key  to  the  nervous  processes 
which  occur  during  excitement. 

In  examining  the  changes  in  tension  which  take 
place  during  electrotonus,  the  differences  in  tension 
already  existing  at  the  various  points  must  of  course 
be  taken  into  consideration.  If  the  diverting  arch  is 
applied  to  two  symmetrical  points  of  the  nerve,  they 
are  homogeneous.  If  it  is  applied  to  any  other  points, 
the  existing  differences  in  tension  can  be  cancelled  by 
the  method  of  compensation  above  described  (chap.  x. 
§  4).  The  differences  in  tension  due  to  electrotonus 
are  then  seen  unmixed.  In  all  other  cases  these  dif- 
ferences express  themselves  in  the  form  of  an  increase 
or  decrease  in  the  strength  of  the  nerve-cmrent  which 
happens  to  be  present.  Yet  the  law  of  the  changes 
in  tension  is  the  same  in  all  cases. 

6.  As  we  found  certain  points  of  resemblance  be- 
tween nerves  and  glands,  so  the  nerves  of  the  tissue  of 
the  electric  organs,  in  which  in  the  cases  of  the  fishes 
already  mentioned  such  powerful  electric  action  takes 
place,  may  be  classed  with  these.  Without  entering 
deeply  into  the  researches,  as  yet  very  incomplete, 
which  have  been  made  into  the  structure  of  these 
electric  organs,  we  may  yet  accept  as  already  proved 
that  the  so-called  electric  plate — a  delicate  membran- 
ous structure,  very  many  of  which,  arranged  side  by 
side  and  under  one  another  in  regular  order,  constitute 


ELECTRIC   TISSUE    OF   FISHES.  223 

the  whole  organ — is  to  be  regarded  as  the  basis  of  the 
organ.  A  nerve-fibre  passes  to  each  electric  plate  ; 
and  under  the  influence  of  irritation,  whether  this  is 
due  to  the  will  of  the  animal  or  to  artificial  irritation 
of  the  nerve,  one  side  of  this  plate  always  becomes 
more  positive,  the  other  more  negative.  As  this  occurs 
in  the  same  way  in  all  the  plates,  the  electric  tensions 
combine,  as  in  a  voltaic  battery,  and  this  explains  the 
very  powerful  action  of  such  organs  as  compared  with 
that  exercised  by  muscles,  glands  and  nerves. 

There  is,  indeed,  a  great  difference  between  the 
last-mentioned  tissues  and  the  electric  tissues  of  elec- 
tric fish.  Muscles,  nerves  and  glands  when  quiescent 
generate  electric  forces,  which  undergo  a  change  during 
activity.  Electric  tissue,  on  the  other  hand,  is  en- 
tirely inoperative  when  quiescent,  and  becomes  elec- 
trically active  only  when  it  is  in  an  active  condition. 
Though  unable  to  explain  this  difference,  we  must  re- 
mark that  it  affords  no  ground  for  the  inference  that 
the  actions  of  these  tissues  are  fundamentally  dif- 
ferent. Whether  a  tissue  exercises  externally  apparent 
electric  action,  depends  on  the  arrangement  of  its  ac- 
tive elements.  But  the  changes  which  occur  during 
their  activity  in  muscles,  glands  and  nerves,  and  also 
in  electric  tissue,  are  evidently  so  similar  that  they 
must  be  regarded  as  related.  An  attempt  will  be  made 
in  the  next  chapter  to  obtain  a  common  explanation  of 
all  these  phenomena. 

7.  It  has  already  been  stated  that  electric  phenomena 
have  been  observed  in  plants  also,  though  we  foimd  no 
sufficient  reason  to  attribute  any  great  physiological 
importance  to  these.  It  therefore  created  much  sur- 
prise when  the  physiologist  Burdon-Sanderson  a  few 


224  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

years  ago  stated  as  the  result  of  his  observations, 
that  in  the  leaves  of  Venus'  Flytrap  {DioncBa  Tiiusci- 
pula),  regular  electric  currents  occur,  which,  during 
the  movement  of  these  leaves,  exhibit  negative  varia- 
ation  exactly  as  do  nerve-currents.  He  was  induced 
to  make  his  observations  by  Charles  Darwin,  who,  in 
the  course  of  his  study  of  insectivorous  plants,  at- 
tempted to  show  an  analogy  between  the  leaf-move- 
ments of  the  Dioncea  and  the  muscular  movements  of 
animals.  Darwin's  observations  have  since  been  pub- 
lished in  detail. •  They  show  the  interesting  fact  that 
in  various  plants  glandular  organs  occur  which  secrete 
juices  capable  of  digesting  albuminous  bodies.  The 
plant  above  mentioned,  Dioncea  muscipula,  is  provided 
with  these  glands;  and  in  addition  to  this  it  is  irri- 
table, as  is  the  Mimosa  pudica  described  in  the  first 
chapter.  When  an  insect  touches  the  leaf,  the  halves 
of  the  leaf  close  on  e;ich  other,  and  the  imprisoned 
insect  is  digested  and  absorbed  by  the  secreted  juice. 
In  judging  of  the  nature  of  these  leaf-movements,  it  is 
necessary  to  decide  whether  they  are  really  analogous 
to  muscle-movements,  and  whether  the  identity  extends 
even  to  the  electric  phenomena,  as  Burdon-Sanderson 
would  have  us  believe.  Recent  researches  by  Professor 
Munk  of  Berlin  have  not  confirmed  this.  The  move- 
m.ents  of  the  leaf  of  the  Dioncea  must  be  regarded  as 
entirely  similar  to  those  of  the  Mimosa  pudica.  These 
movements  are  dependent,  not  on  contractions,  as  are 
those  of  muscle,  but  on  curvatures  which  occur  in  the 
leaf  in  consequence  of  an  alteration  in  the  supply  of 
moisture  in  the  different  cell-strata.  The  leaf  does 
indeed  exercise  electric  action,  though  not  in  the  simple 
'   On  Tnsectirorons  Plants.    London,  1875. 


ELECTRIC  ACTION  IN  PLANTS.  225 

way  claimed  by  Burdon-Saiiderson.  Changes  in  the 
electric  action  also  occur  during  the  curvature,  but 
these  changes  do  not  correspond  with  negative  varia- 
tion in  the  nerve-current ;  they  are  probably  connected 
with  the  circulation  of  the  sap  within  the  leaf.  From 
my  own  study  of  Mimosa  jpudica  I  had  already  adopted 
similar  views.  In  this  plant  I  was  unable  to  detect 
regidar  electric  action  during  quiescence  ;  but  on  the 
falling  of  the  leaf-stalk,  I  observed  electric  currents 
which  might  be  explained  as  the  result  of  the  circu- 
lation of  the  sap.  We  must,  therefore,  be  content  to 
accept  the  fact  that  electric  phenomena  in  plants  are 
not  to  be  classed  with  those  observed  in  muscles, 
glands,  nerves,  and  in  the  electric  organs  of  certain 
fishes. 


11 


226         physioijOGY  of  muscles  and  nekves. 


CHAPTER  XIV. 

1.  General  summary ;  2.  Fundamental  explanatory  principles ;  3. 
Comparison  of  muscle-prism  and  magnet ;  4.  Explanation  of  the 
tension  in  muscle-prisms  and  muscle-rhombi ;  5.  Explanation 
of  negative  variation  and  parelectronomy  ;  6.  Application  to 
nerves  ;  7.  Application  to  electric  organs  and  glands. 

1.  Summing  up  the  most  important  facts  given  in 
the  foregoing  chapters,  we  may  make  the  following 
statements  : — 

(1)  Every  Tnuscle,  and  every  part  of  a  muscle,  tvhen 
quiescent,  is  positive  on  its  longitudinal  section; 
negative  on  its  cross-section.  In  a  regular  muscle- 
prism,  the  positive  tension  decreases  regularly  from 
the  centre  of  the  longitudinal  section  totuard  the  ends ; 
and  the  negative  tension  does  the  same  in  the  cross- 
sections.  In  a  muscle-rhombus  the  distribution  of 
the  tension  is  somewhat  different,  for  in  it  the 
greatest  positive  tension  is  re)noved  toward  the  obtuse 
angle  of  the  longitudinal  section,  the  greatest  negative 
tension  totvard  the  acute  angle  of  the  cross-section. 

(2)  During  the  activity  of  the  muscle  the  diff^erences 
in  tension  decrease. 

(3)  Entire  muscles  often  exhibit  but  slight  differ- 
ences in  tension,  or  even  none  at  all;  but  ive  must 
nevertheless  assume  the  existence  of  electric  opposition 
in  them. 

(4)  Nerves  are  positive  on  the  longitudinal  section. 


SUMMARY.  227 

negative  on  the  cross-section.  The  greatest  positive 
tension  is  in  the  centre  of  the  longitudinal  section. 
During  activity  the  differences  in  tension  decrease. 

(5)  The  elective  plate  of  electric  fish  is,  when  qui- 
escent, electrically  inactive ;  influenced  by  the  nerves, 
the  one  side  becomes  electrically  positive,  the  other 
negative. 

(6)  In  the  glands  the  base  is  pjositive,  the  opening 
or  inner  surface  negative ;  during  activity  the  dif- 
ferences in  tension  decrease. 

These  propositions  state  only  the  most  important  of 
the  conditions  which  have  been  shown  by  experiment. 
On  the  outer  surfaces  of  the  tissues  examined  we  found 
differences  in  electric  tension ;  and  we  found  reason 
to  believe  that  the  causes  of  these  differences  in  tension, 
which  occur  with  great  regularity,  must  be  situated 
within  the  tissues  themselves.  We  now  have  to  dis- 
cover these  causes,  and  this  is  not  so  easy  to  do  as 
it  perhaps  appears  at  first  sight.  Difficult  as  it  may  be 
to  calculate  the  tensions  which  must  prevail  at  each 
point  on  the  outer  surface  of  a  given  body,  within 
Avhich  an  electromotive  force  is  situated,  yet  the  diffi- 
culties in  this  case  may  be  overcome  by  skill.  It  is 
different,  however,  when  the  problem  is  reversed,  when, 
the  distribution  of  the  tension  having  been  experi- 
mentally found,  it  is  required  to  discover  the  seat  of 
the  electromotive  force.  The  difficulty  in  this  case 
consists  in  the  fact  that  the  task  is  undefined,  and 
that  many  very  various  solutions  may  be  found.  More- 
ov^er  the  task  is  rendered  yet  more  difficult  by  the 
fact  that  we  do  not  know  whether  one  or  many  elec- 
tromotive forces  are  present,  situated  in  different  parts 
of  the  body. 


228     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

2.  Let  us  suppose,  for  example,  that  in  the  body 
described  in  Chapter  X.  §  2,  the  distribution  of  the 
tension  which  prevails  on  the  surface  as  the  result  of 
the  electromotive  forces  then  assumed,  has  been  proved. 
Let  us  now  imagine  that  this  particular  electromotive 
force  is  removed,  and  is  replaced  by  another,  situ- 
ated at  any  other  point  in  the  body.  Accordingly,  the 
body  will  be  occupied  by  current-curves  of  different 
form,  corresponding  with  different  iso-electric  curves. 
Consequently,  the  distribution  of  tension  on  the  sur- 
face is  also  quite  different.  A  third  electromotive 
force  situated  at  any  other  point  would  again  involve 
an  entirely  different  distribution  of  the  tension,  and  so 
on.  Helmholtz  has  shown  that  when  many  such 
electric  forces  are  present  at  one  time  in  a  body,  the 
tension  which  actually  prevails  at  each  point  of  the 
surface  is  equal  to  the  sum  of  all  the  tensions  which 
would  be  generated  at  this  point  by  each  of  the  electro- 
motive forces  by  itself.  If,  therefore,  a  certain  distri- 
bution of  tension  has  been  experimentally  found,  it  is 
possible  to  conceive  many  combinations  of  electromotive 
forces  which  might  afford  such  a  distribution  of  tension. 

The  rules  of  scientific  logic  afford  a  standard  by 
which  to  choose  to  which  of  all  these  possible  com- 
binations the  preference  shall  be  given.  The  theory 
selected  must,  in  the  first  place,  be  able  to  explain,  not 
only  one,  but  all  the  circumstances  experimentally 
found.  If  new  facts  are  discovered  by  new  experi- 
ments, then  it  must  be  able  to  explain  these  also,  or  it 
must  be  relinquished  in  favour  of  a  better  theory. 
Secondly,  if  several  theories  seem  equally  to  satisfy  the 
required  conditions,  then  preference  must  be  given  to 
the  simplest  rather  than  to  the  more  complex  theories. 


A    MUSCLE-PRISM    AND    A   MAGNET.  229 

But  in  all  cases  it  must  be  borne  in  mind  that  these 
are  only  theories,  the  value  of  which  consists  in  the 
very  fact  that  they  afford  a  common  point  from  which 
all  the  known  facts  may  be  regarded,  and  that  they 
must  in  no  case  contradict  the  value  of  scientifically 
established  facts.  We  require  such  hypotheses,  partly 
because  they  point  the  way  to  further  research,  and 
thus  greatly  aid  the  advance  of  science ;  and  partly 
because  the  human  understanding  finds  no  satisfaction 
in  the  simple  collection  of  separate  facts,  but  rather 
strives,  wherever  it  has  discovered  a  series  of  such 
facts,  to  bring  these,  if  only  provisionally,  into  reason- 
able connection,  and  to  gain  a  common  point  of  view 
from  which  to  regard  them. 

3.  Turning  now  to  our  task  provided  with  these 
preconceptions,  we  will  at  first  confine  our  attention  to 
muscle.  A  regular  muscle-prism  exhibits  a  definite 
distribution  of  tensions.  But  every  smaller  prism 
which  may  be  cut  from  the  larger  exhibits  the  same 
distribution  of  tensions.  No  limits  to  this  are  as  yet 
known,  for  even  the  smallest  piece  of  a  single  muscle- 
fibre  susceptible  of  examination  is  conditioned  in  this 
respect  just  as  a  large  bundle  of  long  fibres.  Two 
possible  explanations  may  be  given  of  this.  It  may 
be  assumed  that  the  electric  tensions  are  due  merely 
to  the  arrangement  of  the  muscle-prism,  or  such  an 
arrangement  of  electromotive  forces  already  present 
in  the  muscle  may  be  conceived  as  explains  all  the 
phenomena  found  to  occur  in  the  muscle.  jNIateucci 
and  others  tried  the  first  of  these  ways.  But  when 
du  Bois-Eeymond  undertook  the  study  of  this  subject, 
and,  with  a  degree  of  patience  and  perseverance  un- 
equalled in  the  history  of  science,  discovered  vei*y  many 


230  PHYSIOLOGY   OF  MUSCLES   AND   NERVES. 

facts,  for  but  a  few  of  which  we  have  been  able  to  find 
place  in  the  foregoing  chapters,  he  was  dissatisfied  with 
this  way,  and,  therefore,  tried  the  second.  And  thus  he 
was  enabled  to  form  an  hypothesis  which  afforded  an 
explanation  of  all  the  previously-known  facts,  of  all 
those  which  have  come  to  light  since  the  hypothesis 
was  first  formed,  and  even  of  some  which  were  first 
indicated  by  the  hypothesis  itself  and  were  then  con- 
firmed by  experiment.  It  is  true  that  attempts  on 
the  other  side  have  since  been  again  made  to  restore 
credit  to  the  older  hypothesis,  but  the  attempts  have 
been  in  vain.  We  shall,  therefore,  fully  accept  the 
hypothesis  constructed  by  du  Bois-Keymond  as  being 
alone  capable  of  including  and  combining  all  electro- 
physiological facts. 

CCCC€€€€)©€©«|c€©€€€C€i)CC)€ 
€C€€€€C€C€€€^C€«)(DCa)®€€€0 
CCCCCCC€i)€0)  ©»)€)€€)€€©«)€©€© 
C€€e€©€€CC©C|©CC€)CC€0©€€0 
b 

Fig.  G1.    Theory  of  jiagxetism. 

The  j)henomenon,  that  when  a  muscle-prism  is  cut 
into  two  halves,  each  part  exhibits  an  arrangement  of 
the  electric  tensions  exactly  analogous  to  that  which 
before  prevailed  in  the  entire  prism,  recalls  a  corre- 
sponding phenomenon  observed  in  the  magnetic  rod. 
It  is  a  well-known  fact  that  every  magnetic  rod  has  two 
poles,  a  north  pole  and  a  south  pole.  The  magnetic 
tension  is  greatest  at  these  two  poles,  and  decreases 
towards  the  centre ;  and  at  the  actual  centre  it  =  0. 
If  the  magnet  is  then  cut  through  in  the  centre,  each 
half  becomes  a  complete  magnet,  with  a  north  and  a 


A   MUSCLE-PRISM   AND   A   MAGNET. 


231 


south  pole,  and  exhibits  a  regular  decrease  of  the  mag- 
netic tensions  from  the  poles  to  the  centre.  However 
often  the  magnet  is  subdivided,  each  fragment  is  always 
a  complete  magnet  with  two  poles,  and  a  regularly 
decreasing  tension.  To  explain  this,  it  is  assumed  that 
the  whole  magnet  consists  entirely  of  small  particles 
(molecules),  each  of  which  is  a  small  magnet  with  a 


ic^n^^ris 


Fig.  C2.     Diagram  of  a  viece  of  muscle-fibue. 


north  and  a  south  pole.  These  small  molecular  mag- 
nets being  all  arranged  in  the  same  order,  somewhat 
as  is  shown  in  figure  61,  they  act  in  combination  in 
the  whole  magnet ;  but  each  separate  part  also  acts  in 
the  same  way. 

The  muscle  may  be  similarly  conceived.  A  stri- 
ated muscle  consists  of  fibres,  all  of  which  in  the  case 
of  a  regular  muscle-prism  run  parallel  to  each  other, 
and  are  of  equal  length.  Each  fibre  must  be  regarded, 
according  to  that  which  was  said  in  Chapter  I.  §  2,  as 


232  PHYSIOLOGY   OF   MUSCLES   AND   KERVES. 

composed  of  regularly  arranged  particles,  each  of  wiiicli 
consists  of  a  small  portion  of  the  simply  refracting 
elementary  substance,  in  which  is  embedded  a  group 
of  the  double-refracting  disdiaclasts.  Such  a  particle 
may  be  called  a  muscle-element.  The  muscle-fibre 
would  accordingly  consist  of  regularly  arranged  muscle- 
elements,  the  sequence  of  which,  in  the  longitudinal 
direction,  forms  the  fibrillae  of  which  mention  has  been 
made;  in  the  lateral  direction  forms  the  discs  into 
which  the  muscle-fibre  may  separate  under  certain 
circumstances.  A  diagram  of  a  piece  of  muscle-fibre 
would,  therefore,  present  an  appearance  somewhat  as 
in  fig.  62,  in  which  each  of  the  small  rectangular 
figures  represents  a  muscle-element.  Each  such  muscle- 
element  is,  therefore,  in  all  essential  points  an  entire 
muscle,  for  the  fibre  is  but  an  accumulation  of  such 
muscle-elements,  each  exactly  like  the  other  ;  and  the 
whole  muscle  is  but  a  bundle  of  homogeneous  muscle- 
fibres.  In  each  muscle-element  we  must,  therefore, 
recognise  the  presence  of  all  the  qualities  which  belong 
to  the  whole  muscle.  It  possesses  the  capacity  of 
becoming  shorter,  and  at  the  same  time  thicker ;  and 
finally — and  this  is  the  gist  of  the  question  here  under 
discussion — it  has  the  same  electric  characters  as  are 
observable  in  the  entire  muscle. 

4.  We  therefore  assume  that  every  muscle-element 
is  the  seat  of  an  electromotive  force,  in  vhtue  of  which 
it  is  positive  on  the  longitudinal  section,  negative  on 
the  cross-section.  If  a  single  muscle-element  of  this 
sort  were  surrounded  by  a  conducting  substance,  sys- 
tems of  current-curves  from  the  side  of  the  longitudinal 
section  to  that  of  the  cross-section  would  be  present 
within  it.     If  many  such  muscle-elements  are  arranged 


TENSIONS   IN    MUSCLE-PRIS.MS    AND    KHOMBI. 


233 


side  bj  side  and  one  behind  the  other  in  the  regular 
arrangement  which  we  have  assumed,  then  the  whole 
must,  as  has  been  shown  by  calculation,  be  positive 
throughout  its  longitudinal  section,  negative  through- 
out its  cross-sections.  Xo\y,  si  pposing  that  this  whole 
aggregation  of  muscle-elements  is  surrounded  by  a 
thin  layer  of  a  conducting  substance,  then  currents 
such  as  are  represented  in  fig.  63  must  be  present 
within  it.  These  current-curves  then  accurately  corre- 
spond with  that  distribution  of  the  tensions  which  was 
experimentally  shown.     The  greatest   positive  tension 


" 

i 

^  i 

- -^      _J     _- 

-< 

1^-= 

_,    s^    rz:-,^-^ 

=-.     „. 

.  -J 

^ 

;i> — 

J 

Fig.  G3. 


DiAGRA.M    OF    THE    EI.ECTKIC   ACTIOX    IS    AX   AGGREGATION   OF 
JICSCLE-ELEMENTS. 


must  prevail  in  the  centre  of  the  longitudinal  section ; 
the  greatest  negative  tension  in  the  centre  of  the 
cross  section ;  and  both  must  decrease  in  a  regular  way 
toward  the  edges. 

We  now  take  a  bundle  of  muscle-fib] es,  the  ends 
of  which  are  formed  by  two  artificial  straight  cross- 
sections,  in  other  words,  a  regular  muscle-prism.  The 
separate  muscle-fibres,  which  constitute  the  bundle, 
are  surrounded  by  sarcolemma,  held  together  and  en- 
veloped by  connective  tissue.  JMoreover,  the  outer- 
most strata  must  obviously  become  subject  sooner  than 
the  inner  to  the  unfavourable  influences  of  mortifica- 
tion, which,  as  we  have  seen,  finally  lead  to  the  entire 
loss  of  electric  qualities ;  these  outermost  strata  there- 


234 


PHYSIOLOGY    OF    MUSCLES   AND    NERVES. 


fore  become  quite  inoperative,  or  less  operative  than 
the  inner.  This  injurious  influence  must  be  yet  more 
strongly  developed  on  the  cross-section,  where  a  layer 
of  crushed,  that  is,  dead  muscle-substance,  overlies 
the  parts  which  yet  remain  operative.  Owing  to  all 
these  circumstances,  a  coating  of  inoperative  but  con- 
ducting substance  envelopes  the  operative  muscle- 
elements,  and  the  distribution  of  the  tensions  on  the 
regular  muscle-prism  is  fully  explained.  And  when 
such  a  muscle-prism  is  divided,  the  conditions  always 
remain  unaltered.  Each  part  of  a  muscle-prism  must 
act  as  would  the  whole. 


Fig.  64.    Diagram  of  ax  oblique  ceoss-sectiox. 

Our  hypothesis  is  therefore  quite  able  to  explain 
the  electric  phenomena  of  a  regular  muscle-prism. 
We  must  now  see  how  it  stands  in  relation  to  the  other 
facts  which  we  have  learned.  If  the  artificial  cross- 
section  is  made  obliquely  to  the  axis  of  the  muscle- 
fibres,  as  in  a  regular  or  irregular  muscle-rhombus,  then 
our  assumed  muscle-elements,  at  the  cross-section,  will 
be  arranged  one  over  the  other  like  steps,  and  are 
clothed  by  a  layer  of  crushed,  and  therefore  inopera- 
tive tissue,  as  is  represented  in  fig.  64.  On  such  a 
cross-section  it  is  evident  that  separate  currents  must 
circulate  from  the  positive  longitudinal  section  to 
the  negative  cross-section  of  each  individual  muscle- 
element,  and  these   combine  with  the  current  circu- 


NEGATIVE   VARIATION   AND    PARELECTRONOMY.     235 

lating  from  the  longitudinal  to  the  cross-section  of 
the  entire  prism,  to  make  the  obtuse  angle  more 
positive  than  negative. 

5.  We  must  next  inquire  how  the  negative  varia- 
tion of  the  muscle-current  during  activity  can  be  ex- 
plained in  accordance  with  our  hypothesis.  We  have 
already  found  reason  to  believe,  from  the  phenomena 
of  muscle-tone,  that  the  contraction  of  the  muscle 
depends  on  a  movement  of  its  smallest  particles.  Mi- 
croscopic observation  of  muscular  contraction  shows 
that  the  movement  takes  place  within  each  muscle- 
element,  for  the  change  in  form  may  be  detected  in 
each  muscle-element  just  as  in  the  whole  muscle-fibre. 
It  is  therefore  not  difficult  to  conceive  that,  in  con- 
nection with  these  movements  of  the  smallest  particles 
within  each  muscle-element,  the  electromotive  opposi- 
tion between  the  longitudinal  and  cross-sections  of  that 
element  undergo  a  change.  It  is  of  little  importance 
whether  we  conceive  the  matter  as  though  the  mo- 
lecules of  the  muscle  undergo  vibratory  motion  during 
contraction,  or  whether  we  give  the  preference  to  some 
other  theory.  Where  facts  are  wanting  to  support  or 
contradict  certain  assumptions,  the  imagination  may 
have  free  play,  and  may  picture  any  process  by  which 
changes  of  the  kind  under  consideration  might  pos- 
sibly be  brought  aboiit.  But  the  discreet  man  of 
science,  while  allowing  himself  this  liberty,  ever  re- 
members that  such  free  play  of  the  imagination  is  of 
no  real  scientific  value,  either  didactically,  as  explain- 
ing known  facts,  or  temporarily  as  leading  anti  inciting 
to  new  researches.  Good  hypotheses  are  always  avail- 
able in  both  these  ways,  and  the  scientific  man  uses 
only  such.    lie  may  perhaps  amuse  himself  in  a  leisure 


236  PHYSIOLOGY    OF    MUSCLES   AND    NERVES. 

quarter  of  an  hour  by  allowing  his  imagination  to 
carry  the  hypotheses  further  than  the  point  up  -  to 
which  they  are  based  on  known  facts  ;  but  he  does  not 
presume  to  urge  the  results  on  others. 

Finally,  we  have  to  examine  how  far  the  hypothesis 
to  which  we  have  given  the  preference  is  confirmed  by 
the  phenomena  observable  in  entire  muscles.  The 
tendonous  covering  on  the  ends  of  muscle-fibres  may 
be  regarded  as  a  layer  of  non-active  conducting  sub- 
stance. In  so  far  as  the  same  phenomena  are  ex- 
hibited in  the  uninjured  muscle,  as  in  the  muscle- 
prism  or  muscle-rhombus  with  its  artificial  cross 
section,  nothing  need  be  added  to  the  previous  ex- 
planations. But  this  is,  as  we  have  seen,  though 
generally,  yet  not  always  the  case.  The  natiual  cross- 
section  of  a  muscle  is  generally  very  slightly  negative, 
sometimes  not  at  all,  as  compared  with  the  longi- 
tudinal section ;  but  the  negative  character  becomes 
marked  as  soon  as  the  natural  cross-section  has  been 
destroyed  in  any  way,  either  mechanically,  chemically, 
or  thermically.  In  explanation  of  this  condition  of 
the  natural  ends  of  muscle-fibres,  we  may  assume  that 
the  arrangement  of  the  molecules  in  the  latter  or  in 
the  terminal  muscle-elements  in  each  muscle-fibre  may 
sometimes  be  different  from  that  at  all  other  points. 
If,  for  example,  the  cross-section  in  the  terminal 
muscle-element  were  not  negative,  the  muscle-fibre 
could  atford  no  current,  though  such  a  current  would 
arise  as  soon  as  this  terminal  muscle-element  was  re- 
moved or  was  transforme.d  into  a  non-active  conductor. 
E.  du  Bois-Eeymond  has  lately  succeeded  in  discover- 
ing a  very  probable  reason  for  this  abnormal  condition 
of  the  ends  of  muscle-fibres ;  but  without  entering  too 


THE  NERVES.  237 

deeply  into  details  we  should  not  be  able  to  explain 
this  here.^ 

6.  We  will  now  turn  our  attention  to  nerves.  The 
resemblance  of  the  phenomena  in  the  case  of  muscles 
and  of  nerves  is  so  great  that  it  is  natural  at  once  to 
transfer  the  hypotheses  assiimed  for  the  former  to  the 
latter.  It  is  true  that  in  nerves  there  are  not  the 
microscopically  visible  particles  (the  so-called  muscle- 
elements)  on  which  we  based  our  theory  in  the  case 
of  muscles,  and  in  which  we  recognised  the  presence  of 
electromotive  forces.  But  from  what  we  have  already 
seen  of  the  processes  of  excitement  in  the  nerve,  it  is 
at  least  evident  that  in  the  nerve  also  separate  par- 
ticles, with  independent  power  of  movement  and  inde- 
pendent forces,  must  be  arranged  in  sequence  in  the 
longitudinal  direction  of  the  nerve.  If,  without  being 
able  to  say  anything  further  of  their  nature,  but  be- 
cause of  the  analogy,  we  call  these  particles  nerve- 
elements,  and  if  we  assume  that  each  of  these  nerve- 
elements  is  the  seat  of  an  electromotive  force,  in 
consequence  of  which  the  longitudinal  section  exhibits 
positive  tension,  the  cross-section  exhibits  negative 
tension,  then  the  phenomena  in  the  quiescent  nerve 
and  the  negative  variation  of  the  nerve-current  during 
activity  are  explicable  exactly  as  were  the  correspond- 
ing phenomena  in  muscles.  The  entirely  similar  be- 
haviour of  nerves  and  muscles  when  irritated  is  alone 
sufficient  to  show  satisfactorily  that  the  two  must  be 
very  much  alike  in  their  physical  structure ;  and  the 
similarity  of  their  behaviour,  in  point  of  electromotive 
activity  is  such  as  to  lend  weight  to  our  assumption  of 

'  See  Notes  and  Additions  No.  li. 


238        pm'SioLOGY  of  muscles  and  nerves. 

the  similarity  in   the  arrangement  of  their   smallest 
particles. 

But  together  with  many  points  of  resemblance, 
nerve  and  muscle  exhibit  some  points  of  difference. 
The  muscle  during  activity  changes  its  form  and  is 
able  to  accomplish  work ;  the  nerve  is  incapable  of 
this.  The  nerve,  on  the  other  hand,  under  the  in- 
fluence of  continuous  electric  currents,  exhibits  those 
changes  in  excitability  which  we  observed  under  the 
name  electrotonus,  and  which,  as  we  have  seen,  corre- 
spond with  changes  in  the  distribution  of  the  tensions 
on  the  outer  surface  of  the  nerve.  No  correspond- 
ing phenomena  have  been  shown  in  muscle.  Other 
changes  which  effect  these  changes  in  tension  must, 
therefore,  occur  within  the  nerve-element. 

It  is  a  well-known  fact  that  all  substances  occupy- 
ing space  are  regarded  as  composed  of  small  particles, 
to  which  the  name  molecules  is  given.  In  a  simple 
chemical  body,  such  as  hydrogen,  oxygen,  sulphur,  iron, 
and  so  on,  all  these  molecules  consist  of  homogeneous 
atoms  ;  in  a  chemically  compound  body,  such  as  water, 
carbonic  acid,  and  so  on,  each  molecule  is  composed  of 
several  atoms  of  different  kinds.  A  molecule  of  water, 
for  instance,  consists  of  an  atom  of  oxygen  and  two 
atoms  of  hydrogen ;  a  molecule  of  carbonic  acid  con- 
sists of  an  atom  of  carbon  and  two  atoms  of  oxygen ; 
a  molecule  of  common  salt  consists  of  an  atom  of 
natron  and  an  atom  of  chlorine,  and  so  on.*  A  piece 
of  salt  contains  a  very  large  number  of  such  atoms 
composed  of  chlorine  and  natron,  but  each  of  these 

•  Details  of  the  atomic  and  molecular  theory  will  be  found  in 
'The  New  Chemistry.'  Cooke  (International  ScientlSc  Series, 
vol.  ix.). 


THE   NERVES.  239 

(in  pure  cooking  salt)  is  like  every  other.  But  a 
muscle,  a  nerve,  or  any  other  organic  tissue,  is  much 
more  complex  in  structure.  Molecules  of  albumen, 
of  fats,  of  various  salts,  of  water,  and  so  on,  are 
mingled  in  it.  A  very  small  piece  of  such  a  tissue 
must  be  regarded  from  a  chemical  point  of  view  as  a 
compound  of  very  many  diJSerent  substances.  To  avoid 
confusion,  the  name  '  muscle-element '  or  '  nerve- 
element  '  has  been  given  to  these  particles,  in  which 
we  assume  the  existence  of  all  the  quaHties  of  muscle 
or  nerve,  but  this  name  expresses  nothing  further  than 
a  fragment  of  a  muscle  or  nerve.  Even  such  a  frag- 
ment must  be  regarded  as  of  very  complex  structure. 
Very  complex  physical  and  chemical  processes  may 
take  place  within  it ;  and  the  processes  of  muscle  and 
nerve  activity,  the  actual  nature  of  which  is  as  yet 
quite  unknown  to  us,  are  certainly  connected  with  such 
chemical  and  physical  processes.  If  electric  forces  also 
occur  in  such  a  nerve-  or  muscle-element,  it  is  not  sur- 
prising that  these  also  undergo  various  changes.  Of 
this  sort  must  be  the  changes  which  occur  during  ac- 
tivity and  during  electrotonus. 

In  speaking,  as  we  have  occasionally  done,  of  nerve- 
and  muscle-molecules,  we  have,  therefore,  not  used  the 
term  molecule  quite  in  the  clear  and  fixed  sense  in 
which  the  term  is  used  in  chemistry.  Our  conception 
was  rather  of  something  which,  itself  composed  of  va- 
rious chemical  substances,  forms  a  unit  of  another 
order.  For  the  sake  of  brevity  we  shall  still  sometimes 
use  the  expression  in  this  sense,  as,  after  the  explana- 
tion Avhich  has  now  been  given,  we  may  do  this  without 
fear  of  being  misunderstood.  A  muscle-  or  a  nerve- 
molecule  accordingly  means  a  group  of  chemical  mo- 


240  PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 

lecules  combined  in  a  particular  way,  many  of  which, 
in  combination,  form  a  muscle-molecule  or  a  nerve- 
element  respectively. 

We  have  learned  to  regard  the  negative  variation  of 
the  muscle-  or  nerve-current  as  a  movement  of  these 
muscle-  or  nerve-molecules  respectively,  in  consequence 
of  which  the  differences  in  tension  between  the  longi- 
tudinal and  cross-sections  become  less.  In  explanation 
of  the  electric  phenomena  of  electrotonus,  we  may  now 
assume  that  under  the  influence  of  continuous  electric 
currents  the  nerve-molecules  assume  a  different  relative 
position  by  reason  of  which  the  distribution  of  the 
tensions  on  the  outer  surface  of  the  nerve  is  changed. 
This  changed  position  is  retained  as  long  as  the  electric 
current  flows  through  the  nerve,  and  disappears  more 
or  less  rapidly  after  the  opening  of  the  current.  At 
first  it  takes  effect  only  within  the  electrodes,  but  it 
propagates  itself  through  the  extrapolar  portions,  be- 
coming gradually  weaker  the  further  it  is  from  the 
electrodes.  In  illustration  of  this  conception,  we  may 
avail  ourselves  of  the  comparison  which  we  have  already 
made  of  the  nerve-molecules  with  a  series  of  magnetic 
needles.  When  the  position  of  some  of  the  needles  in 
the  centre  of  such  a  series  is  changed,  owing  to  some 
external  influence,  those  needles  which  lie  more  on  the 
outside  of  the  series  must  be  turned  to  an  extent  de- 
creasing with  their  distance  from  the  centre.  Or  we 
may  also  refer  to  the  conception  which  physicists  have 
formed  of  the  so-caUed  electrolysis,  the  analysis  of  a 
fluid  by  an  electric  current.  All  these  analogies  can 
only  explain  the  process  in  so  far  that  we  recognise  how 
an  electric  current  is  capable  of  causing  a  change  in  the 
relative  position  of  the  muscle-  and  nerve-molecules, 


GLANDS  AND    ELECTRIC   ORGANS.  241 

at  first  only  between  the  electrodes,  but  afterward 
beyond  these,  which  change  then  corresponds  with  a 
change  in  the  distribution  of  tension  on  the  surface. 

7.  We  have  yet  to  consider  how  far  the  hypothesis 
under  discussion  explains  the  electric  phenomena  in 
electric  fishes  and  in  the  glands.  The  electric  shock 
of  the  torpedo  must  evidently  be  regarded  as  analo- 
gous to  negative  variation  in  muscle-  and  nerve- 
currents.  The  apparently  great  difiference  that  in  the 
latter  a  current  present  during  a  state  of  quiescence 
becomes  weaker  during  activity,  while  in  electric  fishes 
an  organ  which  is  entirely  inoperative  during  the  state 
of  quiescence  generates  a  current  when  it  becomes 
active,  appears,  when  closely  examined  from  the  point 
of  view  afforded  by  our  hypothesis,  to  be  of  no  account. 
For,  from  the  fact  that  no  current  in  an  organ  can  be 
externally  shown,  it  by  no  means  follows  that  no  elec- 
tromotive forces  are  present  within  the  organ.  A  piece 
of  soft  iron  is  in  itself  entirely  non-magnetic ;  but  as 
this  may  at  any  time  bo  transformed  into  a  magnet  by 
bringing  a  magnet  into  its  neighbourhood,  or  by  the 
influence  of  an  electric  current,  we  suppose  that  mole- 
cular magnets  are  present  even  in  the  soft  iron,  though 
these  a,re  not  regularly  arranged  as  in  a  regular  magnet, 
such  as  that  represented  in  fig.  61,  p.  230.  The  action 
of  the  magnet  which  is  brought  near,  or  of  the  electric 
current,  therefore  consists  solely  in  the  fact  that  it  ar- 
ranges the  irregularly  placed  molecular  magnets  within 
the  soft  iron,  and  thus  allows  thek  action  to  appear 
externally.  If  no  magnetic  action  were  known  in  soft 
iron,  no  one  would  ever  have  had  an  idea  that  magnetic 
forces  were  present  within  it.  But  comparison  with  the 
permanent  magnet,  and  the  possibility  that  thoroughly 


242  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

non-magnetic  iron  may  at  any  time  be  transformed  into 
a  magnet,  makes  the  involved  conception  quite  natural. 
It  is  exactly  the  same  in  the  case  of  the  electric  organs 
of  the  torpedo.  The  fact  that  they,  though  in  them- 
selves electrically  inoperative,  become  electrically  oper- 
ative under  the  influence  of  the  nerves,  when  combined 
with  what  we  know  of  nerves  and  muscle,  naturally 
leads  us  to  suppose  that  electromotive  forces  are  pre- 
sent in  the  electric  plates,  but  that  they  are  so  ar- 
ranged as  to  cause  no  observable  differences  of  tension 
on  the  outer  surface.  Under  the  influence  of  the  ac- 
tive nerves,  the  particles  endowed  with  electric  forces 
undergo  a  change  in  their  relative  position,  differences 
of  tension  between  the  two  surfaces  of  the  electric  plates 
intervene,  and,  as  all  the  electric  plates  in  an  organ  act 
in  the  same  way,  the  result  is  a  powerful  electric  shock, 
which,  in  spite  of  its  powerful  efifect,  differs  from  the 
negative  variation  of  the  m.uscle-  and  nerve-currents  only 
as  does  the  powerful  current  of  a  many-celled  galvanic 
battery  from  the  weak  current  of  a  small  apparatus. 

In  order  to  make  the  similarity  between  the  electric 
organ  on  the  one  hand,  and  muscles  and  nerves  on  the 
other,  yet  more  prominent,  we  will  carry  the  compari- 
son with  magnetic  phenomena  yet  further.     In  fig.  65, 


A  B  lY  s 

Fig.  65.    Magnetic  ixductiox. 

A  B  isa,  piece  of  soft  iron,  JV  S  a.  magnet  which  we  bring 
from  some  distance  toward  the  iron  rod  A  B.  The  result 
is  to  evoke  magnetism  inAB,A  becoming  a  north  pole, 
and  B  a  south  pole.  Now,  let  us  suppose  that  the  non- 
magnetic iron  rod  AB  i?.  replaced  by  an  entirely  similar, 


GLANDS   AND   ELECTRIC    ORGANS.  243 

but  magnetic  rod  iV,  S^  (fig.  66).  At  the  moment  at 
which  the  magnet  NS  is  brought  near,  the  magnetism 
of  iVj  S^   becomes  weaker,  ceases  entirely,  or  is  even 


,S-,  jV,  A''  S 

Fig.  66.    Magnetic  induction. 

reversed.  The  same  process  of  magnetic  induction  is 
concerned  in  both  cases.  The  only  difference  is  that  in 
one  case  the  induction  seizes  on  an  iron  rod  the  mole- 
cular magnets  of  which  are  irregularly  arranged,  and 
which  therefore  appears  non-magnetic;  while  in  the 
second  case  the  iron  rod  is  in  itself  magnetic.  So  that 
in  one  case  magnetism  is  evoked  by  induction,  in  the 
other,  magnetism  which  was  already  present  is  weak- 
ened ;  but  the  induction  is  the  same  in  both  cases.  In 
just  the  same  way  electric  tensions  are  induced  in  the 
electric  plate  by  the  influence  of  the  nerves,  while  the 
tensions  present  in  the  muscle  are  weakened ;  but  the 
process  in  the  electric  plate  and  in  the  muscle  is  the 
same. 

We  have  now  only  to  say  a  few  words  about  the 
glands.  The  phenomena  in  these  are,  so  far  as  we  can 
infer  from  the  few  known  facts,  so  entirely  like  those  in 
muscles,  that  it  is  only  necessary  to  transfer  the  expla- 
nation which  we  have  given  in  the  case  of  the  muscles 
to  the  glands.  In  each  gland-element  electric  forces 
are  present  which  make  the  base  of  the  gland  positive, 
the  mouth-opening  negative.  When  the  gland  becomes 
active,  these  differences  in  tension  become  less.  There 
is  no  occasion  to  speculate  as  to  how  far  this  affects  the 
process  of  secretion,  as  it  could  not  further  explain  the 
process. 


244  ■         PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 


CHAPTEE  XV. 

1.  Connection  of  nerve  and  muscle;  2.  Isolated  excitement  of 
individual  mnscle-fibres ;  3.  Discharge-hypothesis;  4.  Principle 
of  the  dispersion  of  forces;  5.  Independent  irritability  of  muscle- 
substance;  6.  Curare;  7.  Chemical  irri'ants;  8.  Theory  of  the 
activity  of  the  nerves. 

1.  In  the  foregoing  chapters  we  have  examined  the 
characters  of  muscles  and  nerves  separately.  The 
ni.uscle  is  distinguished  by  its  power  of  shortening  and 
thereby  accomplishing  work.  The  nerve  has  not  this 
power :  it  is  only  able  to  incite  the  muscle  to  activity. 
We  must  now  inquire  how  this  incitement,  this  trans- 
ference of  activity  from  the  nerves  to  the  muscles, 
occurs. 

■  To  understand  the  action  of  a  machine,  of  any  piece 
of  mechanism,  it  is  necessary  to  learn  its  structure  and 
the  relative  positions  of  its  separate  parts.  In  our  case, 
microscopic  observation  can  alone  afford  the  explana- 
tion. If  we  trace  the  course  of  the  nerve  within  the 
muscle,  we  find  that  the  separate  fibres,  which  enter 
the  muscle  in  a  connected  bundle,  separate,  run  among 
the  muscle-fibres,  and  spread  throughout  the  muscle. 
It  then  appears  that  the  single  nerve-fibres  divide,  and 
this  explains  the  fact  that  each  muscle-fibre  is  eventu- 
ally provided  with  a  nerve-fibre — long  nerve-fibres  even 
with  two — although  the  number  of  nerve-fibres  wkich 
enter   the   muscle  is    generally  much    less    than   the 


COXXECTIOX    OF   XERVE   AXD    MUSCLE. 


245 


number  of  the  muscle-fibres  which  compose  the  muscle. 
Till  the  nerve  approaches  the  muscle-fibre,  it  retains  its 
three  characteristic  marks — the  neurilemma,  medullary 
sheath,  and  axis-cylinder.  When  near  the  muscle-fibre, 
the  nerve  suddenly  becomes  thinner,  loses  the  medul- 
lary sheath,  then  again  thickens,  the  neurilemma  co- 


FlG.  67.     TKRMI>fATIONS   OF   XERVES   IX   THE    MUSCLES  OF  A  GL'ISEA-PIO. 

alesees  with  the  sarcolemma  of  the  muscle-fibre,  and 
the  axis-cylinder  passes  directly  into  a  structure  which 
lies  within  the  sarcolemma  pouch,  in  immediate  con- 
tact with  the  actual  muscle-substance,  and  is  called  the 
terminal  nerve-plate.  Fig.  67  represents  this  passing 
of  the  nsrve  into  the  muscle  as  it  occurs  in  mammals. 
In  other  animals  the  form  of  the  terminal  plate  is  some- 


246  PHYSIOLOGY    OF   MUSCLES   AND   NEKVES. 

what  different ;  but  the  relation  between  the  nerve  and 
the  muscle  is  the  same.  The  essential  fact  is  the  same 
in  all  eases :  the  nerv^  passes  into  direct  contact 
with  the  muscle- substance.  All  observers  are  now 
agreed  on  this  point.  Uncertainty  prevails  only  as  to 
the  further  nature  of  the  terminal  plate.  In  the  frog, 
for  instance,  there  is  no  real  terminal  plate,  but  the 
nerve  separates  within  the  sarcolemma  into  a  net-like 
series  of  branches,  which  can  be  traced  for  a  short  dis- 
tance from  the  point  of  entrance  in  both  directions. 
Professor  Gerlach  has  recently  declared  that  this  net, 
as  well  as  the  terminal  nerve-plate,  are  not  really  the 
ends  of  the  nerves,  but  that  the  nerve  penetrates 
throughout  the  muscle-substance,  and  that  throughout 
the  whole  muscle-fibre  there  is  an  intimate  imion  of 
nerve  and  muscle. 

2.  However  this  may  be,  the  fact  that  the  nerve- 
substance  and  the  muscle-substance  are  in  immediate 
contact  must  serve  as  the  starting-point  from  which  to 
attempt  an  explanation.  When  it  was  thought  that 
the  nerve  remained  on  the  outer  surface  of  the  muscle- 
fibre,  there  was  difficulty  in  explaining  how  a  pulsation 
of  individual  muscle-fibres  within  a  muscle  could  be 
elicited  by  irritation  of  individual  fibres  of  a  nerve. 
For  the  nerve-fibres,  in  their  course  within  the  muscle, 
touch  externally  many  muscle-fibres,  over  which  they 
pass  before  they  finally  end  at  another  muscle-fibre. 
In  the  case  of  flat,  thin  muscles,  it  may  be  shown  con- 
clusively that  such  a  nerve-fibre  may  be  irritated  in 
such  a  way  that  those  muscle-fibres  over  which  it 
passes  remain  quiescent,  and  only  those  pulsate  at 
which  the  nerve-fibre  ends.  As  soon,  however,  as  it  is 
understood  that  the  excitement  present  in  the  nerve- 


THE    DISCHARGE    HYPOTHESIS.  247 

fibre  cannot  penetrate  through  the  sheaths,  it  is  clear 
that  the  excitement  can  only  act  on  the  muscle- 
substance  where  the  nerve-substance  and  the  muscle- 
substance  are  really  in  immediate  contact — that  is,  only 
within  the  sarcolemma  pouch.  The  nerve-sheath  is,  as 
we  already  know,  a  real  isolator  as  regards  the  process 
'of  excitement  within  the  fibre ;  for  an  excitement  within 
a  nerve-fibre  remains  isolated  in  this,  and  is  not  trans- 
ferred to  any  neighbouring  fibre.  It  is  quite  impos- 
sible, therefore,  that  it  can  transfer  itself  to  the  muscle- 
substance,  since  it  is  separated  from  the  latter  not  only 
by  the  nerve-sheath,  but  also  by  the  sarcolemma. 

But  if  the  nerve-fibre  penetrates  the  sarcolemma,  as 
appears  from  the  microscopic  observations  above  de- 
scribed, and  if  nerve-substance  and  muscle-substance 
are  in  immediate  contact,  then  the  transference  of  the 
excitement  present  in  the  nerve  to  the  muscle  substance 
is  intelligible.  The  argument  holds  good  whether  we 
assume  that  the  nerve,  directly  after  its  entrance  within 
the  sarcolemma,  ends  in  a  nerve -plate  or  a  short  nerve- 
net,  or  whether,  as  Gerlach  says,  it  spreads  further.  All 
that  is  needed  to  make  the  process  of  transference  in- 
telligible is  that  the  two  substances  should  be  in  imme- 
diate contact,  and  so  much  is  granted,  whichever  view 
is  preferred.  But  the  process,  if  intelligible,  is  yet  not 
explained.  An  attempt  at  explanation  must  be  based 
on,  and  have  regard  to,  all  the  established  facts. 

3.  It  is  natm-al  to  think  of  the  electric  characters 
of  nerves  and  muscles,  and  to  seek  the  explanation  in 
these.  In  nerves  electric  tensions  prevail  which  dur- 
ing the  activity  of  the  nerve  undergo  a  sudden  decrease, 
a  so-called  negative  variation.  Such  sudden  variations 
of  electric  currents  are,  we  know,  able  to  excite  the 


248  PHYSIOLOGY    OF   MUSCLES   AND    NERVES 

muscle.  We  may,  therefore,  conceive  the  process  som.e- 
what  as  follows.  The  excitement  in  the  nerve,  however 
caused,  propagates  itself  along  the  nerve-fibre  until  it 
reaches  the  end  of  the  latter.  Connected  with  it  is  an 
electric  process,  by  which  a  sudden  electric  variation 
is  caused  in  the  terminal  apparatus  of  the  nerve- 
fibre,  and  this  excites  the  nerve-substance,  just  as  a 
shock  acting  externally  immediately  on  the  muscle 
would  excite  it. 

Following  du  Bois  Eeymond,  the  above  conception 
may  be  called  the  discharge-hypothesis  {Entladivngs- 
hypothese).  According  to  it,  the  muscle  end  of  a  nerve- 
fibre  must  be  regarded  as  similar  to  an  electric  plate 
in  the  pecuhar  organs  of  electric  fish.  Indeed,  in  the 
latter,  an  electric  discharge  is  effected  by  the  influence 
of  nerve-excitement,  which  is  able  to  cause  other  excit- 
able structures,  such  as  muscles  and  glands,  to  contract. 
We  do  not  attach  any  weight  to  the  accidental  external 
resemblance  of  the  terminal  nerve-plate  to  the  electric 
plate.  In  frogs  and  many  other  animals  there  are  no 
terminal  plates,  and  yet  the  conditions  are  the  same  in 
their  case  also.  And  even  if  the  view  upheld  by  Gerlach 
is  confirmed,  and  it  is  shown  that  nerve-substance  comes 
into  more  intimate  contact  with  muscle-substance  than 
merely  at  the  point  at  which  it  enters  the  muscle- 
pouch,  our  explanation  will  be  unaffected.  All  that  we 
claim  is  that  an  electric  discharge,  by  which  the  muscle- 
substance  is  irritated,  takes  place  in  the  terminal  expan- 
sions of  the  nerves,  of  w^hatever  form  these  expansions 
may  be. 

Against  the  acceptance  of  this  view  a  difficulty  at 
first  seems  to  present  itself  in  the  fact  that  such  an 
electric  shock,  taking  place  in  the  end  of  a  nerve,  would 


THE  FREEING  OF  FORCES.  249 

excite  not  only  the  muscle-fibre  in  whicli  the  nerve 
ends,  but  the  adjacent  fibres  also.  For  in  the  muscle 
and  its  envelopes  no  electric  isolators  are  present,  and 
an  electric  shock,  occurring  at  any  point,  can  and  must 
spread  throvighout  the  whole  muscle  mass.  But  from 
the  law  of  the  distribution  of  currents  in  irregular  con- 
ductors, the  essential  outlines  of  which  are  given  in  the 
twelfth  chapter,  it  apjjears  that  the  strength  of  the  cur- 
rent in  the  immediate  neighbourhood  of  the  spot  at 
which  the  discharge  actually  takes  place  may  be  con- 
siderable, though  it  decreases  so  rapidly  with  increasing 
distance,  that  it  is  easy  to  believe  that  it  may  be  quite 
unnoticeable,  even  in  a  muscle-fibre  which  stands  side 
by  side  with  the  fibre  directly  irritated.  It  is  this 
very  circumstance  which  lends  especial  weight  to  the 
fact  that  the  nerve  penetrates  within  the  muscle-fibre, 
and  there  comes  into  immediate  contact  with  the  muscle- 
substance.  Only  in  this  way  is  it  intelligible  that  a 
discharge  occurring  in  the  nerve  can  irritate  the  muscle. 
When  the  excitement  has  once  arisen  at  any  point 
within  the  muscle-substance,  it  can,  as  we  have  seen, 
spread  within  the  muscle-fibre.  It  is  possible  that  this 
may  result  without  any  co-operation  of  the  nerve-sub- 
stance ;  so  that  the  spreading  of  the  nerve  within  the 
muscle-substance,  as  claimed  by  Gerlach,  is  not  required 
to  explain  the  processes  within  the  muscle.' 

4.  We  therefore  assume  that  the  excitement  aris- 
ing in  the  nerve  itself  becomes  an  irritant,  which 
then  irritates  the  muscle.  The  forces  which  are  gene- 
rated, in  consequence  of  this,  in  the  muscle  are,  as  we 
know,  able  to  accomplish  considerable  labour,  which 
bears  no  relation  to  the  insignificant  forces  which  act 

'  See  Notes  and  Additions,  No.  15. 
12 


250  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

on  the  nerve  and  which  are  active  in  the  nerve  itself 
while  the  latter  transmits  the  excitement.  To  use  a 
common  but  appropriate  simile,  the  nerve  is  but  the 
spark  which  causes  the  explosion  in  the  powder-mine ; 
or,  to  carry  the  simile  further,  the  sulphur  train  which, 
being  fired  at  one  end,  carries  the  fire  to  the  mine,  and 
there  causes  the  explosion.  The  forces  which  are  set 
free  within  the  muscle  are  chemical,  due  to  the  oxida- 
tion of  its  substances  ;  the  irritant  originating  from  the 
nerve  is  only  the  incitement  in  consequence  of  which 
the  chemical  forces  inherent  in  the  muscle  come  into 
play.  Physicists  call  such  processes  the  freeing  of 
forces.  The  nerve-irritant,  therefore,  frees  the  muscle- 
forces,  and  these  translate  themselves  into  warmth  and 
mechanical  work.  In  every  such  freeing,  the  freeing 
force  is  generally  very  small  when  compared  with  the 
forces  set  free,  and  which  may  be  dormant  for  incalcu- 
lable periods ;  though  when  they  are  once  set  free,  they 
are  capable  of  enormous  effects.  A  huge  block  of  stone 
may  for  years  hang  in  unstable  equipoise  on  the  edge 
of  a  precipice  till  some  insignificant  disturbance  makes 
it  fall,  carrying  destruction  to  all  in  the  way  of  its  de- 
scent. It  is  even  supposed  that  the  slight  disturbance 
caused  in  the  air  by  the  sound  of  a  mule-bell  is  suf- 
ficient to  start  the  ball  of  snow  which  at  last  thunders 
down  into  the  valley  in  the  form  of  a  mighty,  all- 
destroying  avalanche.  This  freeing  by  small  forces  is 
only  possible  in  the  case  of  unstable  equipoise.  But 
there  is  also  a  chemical  unstable  equipoise.  Carbon 
and  oxygen  may  lie  for  thousands  of  years  side  by  side 
without  combining.  Closely  mingled,  as  in  gunpowder, 
or  still  more  closely,  as  in  nitro-glycerine,  they  are  in 
unstable  equipoise ;  the  slightest  blow  suffices  to  cause 


INDEPENDENT   lERITABILIT i'    OF   MUSCLES.  251 

their  combination,  which  by  their  expansion  is  able  to 
accomplish  such  gigantic  work.^  In  muscle,  too,  carbon 
and  oxygen  lie  side  by  side  in  chemical  unstable  equi- 
poise ;  and  it  is  the  irritation  of  the  nerves  which  effects 
the  solution  which  destroys  the  equilibrium.  An  arrange- 
ment such  as  that  just  described  is  called  sensitive, 
because  even  an  insignificant  disturbance  is  sufficient  to 
disturb  the  unstable  equipoise  and  to  develop  force.  The 
muscle  is  therefore  a  sensitive  machine.  But  the  nerve 
is  in  a  yet  higher  degree  sensitive,  for  the  smallest  dis- 
turbance of  its  equipoise  gives  play  to  the  forces  within 
it.  But  these  forces  are  in  themselves  incapable  of  any 
great  effects.  They  would  hardly  be  indicable,  were 
not  this  sensitive  machine,  which  we  call  the  nerve, 
connected  with  the  machine,  also  sensitive,  which  we 
call  muscle,  in  such  a  way  that  the  activity  of  the  one 
sets  free  the  forces  within  the  other. 

5.  A  sensitive  machine  is  not  equally  sensitive  to 
all  possible  disturbances.  Dynamite  ^  may  be  placed 
on  an  anvil  and  hammered  without  exploding ;  or,  if 
lighted  with  a  cigar,  it  burns  quietly  out  like  a  fire- 
work. But  when  it  comes  in  contact  with  the  spark  of 
a  percussion  cap,  it  explodes,  and  develops  its  gigantic 
forces.  A  nerve  is  sensitive  to  electric  shocks,  and  to 
certain  mechanical,  chemical,  and  thermic  influences. 
It  is  not  sensitive  to  many  other  influences.  The  in- 
fluences to  which  the  nerve  is  sensitive  we  have  called 
irritants.  A  muscle  is  sensitive  to  electric  shocks,  to 
certain  mechanical,  chemical,  and  thermic  influences ; 

'  On  these  processes  see  Balfour  Stewart  *  On  the  Conservation 
of  Energy '  (International  Scientific  Series,  vol.  vi.)  ;  and  Cooke 
on  '  The  New  Chemistry '  (same  series,  vol.  ix.). 

2  Dynamite  is  a  mixture  of  nitro-glycerine  wilh  'kiesclguhr,'  an 
earth  consisting  of  the  shells  of  infusoria. 


252  Pm^SIOLOGY    OF   MUSCLES   AND   NEEVES. 

and,  above  all,  to  the  influence  of  the  active  nerve. 
The  latter  may  perhaps,  as  we  have  explained  in  the 
foregoing  paragraphs,  be  refeiTed  back  to  electric  irri- 
tation. It  is  thus  apparent  that  muscle  and  nerve 
behave  essentially  in  the  same  "way  towards  irritants. 
But,  remembering  that  nerves  run  for  part  of  their 
course  within  the  muscle,  between  its  fibres,  and  even 
penetrate  within  the  very  muscle-fibres,  the  thought 
now  suggests  itself,  that  perhaps  the  muscle  is  in  no 
way  electrically,  chemically,  thermically,  or  mechani- 
cally irritable ;  perhaps,  when  these  irritants  are  allowed 
to  act  on  the  muscle,  it  is  only  the  intra-muscular  nerves 
which  are  irritated,  and  which  then  in  turn  act  on  the 
muscle-fibres.  In  other  words,  we  have  to  determine 
whether  the  muscle  is  only  irritable  mediately  through 
the  nerves,  or  whether  it  is  also  immediately  irritable, 
independently  of  the  nerves,  by  any  irritants. 

The  question  is  not  a  new  one.  Albert  von  Haller, 
poet  and  physiologist  (1708-77),  asked  it,  and  even  he 
was  not  the  first  to  do  so.  Haller  declared  himself  in 
favour  of  the  second  of  the  two  above-mentioned  possi- 
bilities. He  called  this  capacity  of  the  muscles  to  re- 
ceive independent  irritation  (Irritabilitat),  and  the  name 
has  been  retained.  Haller  met  with  much  opposition 
from  his  contemporaries  ;  and  a  dispute  arose  which  has 
lasted  to  the  present  time.  In  Haller's  days,  of  course, 
only  the  larger  nerve-branchings  were  known.  The 
fiurther  the  nerves  can  be  traced  by  means  of  the  micro- 
scope, the  harder  does  it  evidently  become  to  determine 
the  question  under  discussion. 

6.  In  the  year  1856,  the  French  physiologist  Claude 
Bernard  made  experiments  with  a  poison  brought  from 
Guiana,  which  the  Indians  of  that  region  use  to  poison 


CUEAEE.  253 

their  arrows.     It  is  called  curare,  ourari,  or  Avurali,  and 
is  a  brown,  condensed  plant  juice,  which  is  brought  over 
in  hollowed,  gourd-like  fruits  called  calabashes.     He 
found  that  animals  poisoned  with  this  curare  are  dis- 
abled, and  that  in  animals  thus  disabled,  irritation  of 
the  nerve- trunks,  even  with  the  strongest  electric  or 
other    irritants,    is    entirely   ineffective,    though    the 
muscles  are  yet  easily  irritable.     This  was  indeed  no 
new  phenomenon.      Harless,  at  ]\Iunich,  had  already 
observed  something  similar  in  strongly  etherised  ani- 
mals.    But  soon  afterwards,   Koelliker,   at  Wiirzburg, 
and,    simultaneously,   Bernard   himself,    in    extending 
the  experiments  of  the  latter,  found  something  new. 
If  ligatures  are  applied  to  the  hough  of  a  frog,  and 
the  animal  is  then  poisoned  with  curare,  the  lower  leg 
is  not  disabled.     By  irritation  of  the  sciatic  nerve  the 
muscles  of  the  lower  leg  may  be  induced  to  contract 
where  the  poison  could  not  penetrate,  the  appropriate 
vessels    being  tightly  constricted.     Curare,  therefore, 
does  not  disable   the  muscles,   for   these  always   and 
everywhere  remain  irritable ;  nor  does  it  disable   the 
nerve-trunks,  for  these  remain  irritable  if  the  poison 
cannot  reach  the  muscles.    There  is  but  one  other  thing 
possible :  the  poison  disables  something  which  is  be- 
tween the  nerve-trunk  and  the  muscle-fibre,  so  that  the 
nerve-trunk  can  no  longer  act  on  the  muscle.     If  that 
which  is  disabled  is  the  end  of  the  nerve,  then  the  im- 
mediate irritability  of  the  muscle-substance,  without 
the  participation  of  the  nerves,  about  which  there  has 
been  so  much  strife,  is  proved. 

This  striking  phenomenon  is  not  solitary.  The 
action  of  some  other  poisons,  such  as  nicotine  and 
coniue,  is  entirely  like  that  of  curare.     These  also  dis- 


254  PHYSIOLOGY   OF  MUSCLES   A]S"D   NERVES. 

able,  not  the  nerve-trunks  or  the  muscle-substance,  but 
some  part  intermediate  between  these  two.  The  diffi- 
culty is  to  prove  that  this  part  is  exactly  the  final  termi- 
nation of  the  nerves.  Assuming  that  these  poisons 
disable  some  part  which  lies  between  the  nerve-trunk 
and  the  muscle,  but  not  the  very  end  of  the  nerve,  then, 
though  all  the  phenomena  explained  above  are  quite 
intelligible,  yet  no  answer  has  been  gained  to  the  ques- 
tion of  irritability,  which  we  are  discussing. 

Considering  now  the  characters  of  the  nerve,  and  of 
its  passage  into  the  nerve-fibre,  it  is  easy  to  understand 
why  the  poison  does  not  take  effect  on  the  nerve-trunks. 
The  nerve-fibres  receive  but  few  blood-vessels,  so  that 
the  poison  in  solution  in  the  blood  can  only  reach  them 
slowly,  and  in  very  small  quantity.  Moreover,  the 
fatty  medullary-sheath  probably  forms  a  sort  of  protec- 
tive envelope  round  the  axis-cylinder.  But  where  the 
nerve  enters  the  muscle-fibre  it  loses  the  medullary 
sheath  :  and  just  at  this  same  point  a  very  complex  net 
of  blood-vessels  is  present.  Probably,  therefore,  it  is 
exactly  the  terminal  nerve-plate  (or  the  corresponding 
nerve-branchings  in  the  naked  amphibia)  which  is  most 
exposed  to  the  attack  of  the  poison.  So  long,  however, 
as  it  is  impossible  to  prove  that  this  is  really  the  actual 
end  of  the  nerve-fibre,  a  chance  is  left  open  to  the  op- 
ponents of  the  theory  of  irritability. 

Great  pains  have  been  taken  to  settle  this  point 
with  certainty.  If  a  muscle  poisoned  with  curare  is 
compared  with  a  similar  but  unpoisoned  muscle,  it  ap- 
pears that  the  former  is  less  excitable  ;  that  is,  that 
stronger  irritants  are  needed  to  cause  it  to  pulsate. 
The  explanation  of  this  may  be  that  the  muscls-sub- 
stance  is  excitable,  but  not  so  much  so  as  the  intra- 


CHEMICAL    IRRITANTS.  255 

muscular  nerves.  The  following  reasons  may  also  be 
given  for  the  probability  of  the  independent  irritability 
of  muscle-substance.  A  nerve  is,  as  is  known,  strongly 
excited  by  short,  sudden  variations  of  a  current,  and  an 
unpoisoned  muscle  behaves  in  the  same  way;  but  a 
muscle  poisoned  with  curare  is  less  sensitive  to  current, 
shocks  of  short  duration  than  to  such  as  take  place 
more  slowly.  If  we  ascribe  independent  irritability 
to  muscle-substance,  then  greater  sluggishness  prevails 
in  muscle-substance  than  in  nerve-substance,  so  that 
the  irritating  influences  require  longer  time  to  take 
effect  in  the  former.  In  the  case  of  nerves  it  has, 
moreover,  been  shown  that  currents  which  pass  at  right 
angles  to  the  longitudinal  direction  of  the  nerve-fibre 
are  entirely  ineffective.  In  muscles  under  the  influence 
of  curare  no  difference  in  this  point  can  be  shown.  If 
the  independent  irritability  of  muscle-substance  is  de- 
nied in  spite  of  this,  it  must  be  assumed  that  in  these 
experiments  the  point  lies  in  differences  between  the 
nerve-fibres  and  their  real  ends.  But  nerves  and  muscles 
are  evidently  very  similar,  and  it  might  evidently  be 
possible  to  assume  considerable  difference  between 
nerve-fibres  and  nerve-ends,  and  that  these  ner\e-ends 
differ  from  the  muscle-substance  in ,  nothing  but  that 
the  power  of  being  irritated  is  ascribed  to  the  former, 
while  it  is  denied  to  the  latter.  It  appears  then,  that 
the  whole  dispute  resolves  itself  into  an  empty  word- 
strife  as  to  whether  this  thing  which  lies  between  the 
nerve-fibres  and  the  muscle-substance  is  to  be  reckoned 
as  part  of  the  nerve  or  as  part  of  the  muscle. 

7.  The  much-discussed  question  of  the  independent 
irritability  of  muscle-substance  is,  as  appears  from  what 
has  now  been  said,  due  principally  to  the  fact  that  the 


256  PHYSIOLOGY    OF   MUSCLES   AND    NEEVES. 

same  irritants  wtiich  act  on  the  nerve  are  also  able  to 
act  on  a  muscle,  and  even  on  a  muscle  poisoned  with 
curare.  We  have,  however,  found  slight  differences, 
and,  if  it  were  possible  to  show  the  existence  of  greater 
differences,  especially  if  irritants  were  found  which  act 
on  muscle-substance  but  not  on  nerve-substance,  a  new 
point  of  departure  would  be  gained  for  this  theory  of 
independent  irritability.  Chemical  irritants  are  beyond 
all  others  capable  of  variation.  From  the  endless  num- 
ber of  chemical  bodies  we  may  choose  such  as  irritate 
the  nerve  or  muscle  in  general,  and  we  may  try  each  of 
these  in  every  degree  of  concentration.  If  differences 
between  nerve-substance  and  muscle-substance  really 
exist,  it  is  probable  that  we  shall  find  them  by  these 
means.  Starting  from  these  premisses,  Kiihne  experi- 
mented on  the  condition  of  nerves  and  muscles ;  and 
he  was  so  far  successful  that  he  discovered  some  dif- 
ferences. 

In  studying  the  character  of  nerves  and  muscles 
relatively  to  chemical  irritants,  it  is  best  to  make  a 
cross-section,  and  to  apply  the  substance  which  is  to 
be  tested  to  this  section.  It  is  best  to  apply  the  test 
to  a  thin  parallel-fibred  muscle,  usually  to  the  musculus 
sartoriiis  of  the  upper  leg.  It  is  suspended  upside 
down  from  a  vice,  which  holds  fast  its  lower  pointed 
tendon;  and  its  upper  end,  which  now  hangs  down- 
ward, is  then  cut.  The  liquid  which  is  to  be  tested  is 
then  brought  in  contact  with  the  cross-section  thus 
made,  and  care  is  taken  to  observe  whether  a  pulsa- 
tion takes  place  or  not.  The  short,  used  portion  having 
then  been  cut  off,  the  experiment  can  be  repeated, 
and  so  on  till  the  whole  length  of  the  muscle  has  been 
used.    The  nerve  is  treated  similarly ;  the  sciatic  nerve 


CHEMICAL    IRRITANTS.  257 

is,  as  in  all  experiments  by  irritation,  used  for  the  pur- 
pose, either  in  connection  with  the  whole  lower  leg,  or 
only  with  the  calf-muscle.  If  the  effect  of  volatile 
bodies — vapom-s  or  gases — is  to  be  tested,  the  muscle 
must  be  shut  off  from  the  nerve  in  an  adequate  manner. 

The  muscle  is  extraordinarily  sensitive  to  certain 
substances.  One  part  of  hydrochloric  acid  in  from  one 
thousand  to  two  thousand  parts  of  water  affords  strong 
pulsations.  The  smallest  trace  of  ammonia  is  enough 
to  cause  strong  contraction.  The  observer  must  there- 
fore abstain  from  smoking  whilst  experimenting,  for 
the  slight  amount  of  ammonia  in  tobacco-smoke  is  suf- 
ficient to  elicit  continued  pulsations.  The  nerve,  on 
the  contrary,  is  much  less  sensitive  towards  hydro- 
chloric acid,  and  is  not  at  all  sensitive  towards  am- 
monia. If  the  nerve  is  immersed  in  the  strongest 
solution  of  ammonia  it  very  soon  dies,  but  is  not  at 
all  irritated.  These  are  the  most  marked  differences. 
But  it  must  also  be  mentioned  that  glycerine  and  lactic 
acid  in  concentration  exercise  an  irritating  effect  on  the 
nerve,  but  not  on  the  muscle ;  and  that  when  many 
other  substances  (alkalies,  salts)  are  applied,  small  dif- 
ferences are  exhibited,  in  that  sometimes  the  nerves, 
sometimes  the  muscles,  contract  in  response  to  a  some- 
what thinner  concentration. 

It  thus  appears  that  the  differences  are  extremely 
slight.  Kiihne,  however,  attaches  weight  to  these,  and 
interprets  them  as  favourable  to  the  theory  of  the  in- 
dependent irritability  of  muscle-substance.  He  sup- 
ports this  conclusion  by  the  following  observations.  In 
the  case  of  specific  muscle-irritants  (ammonia,  greatly 
diluted  hydrochloric  acid)  the  result  is  the  same  whether 
the  experiment  is  tried  on  an  ordinary  muscle,  or  on 


258      PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

one  poisoned  witli  curare.  Nor  does  it  make  any  dif- 
ference whether  a  strong  ascending  current  is  passed 
through  the  nerve  of  a  sartorius  thus  conditioned,  thus 
inducing  strong  anelectrotonus  in  the  intra-muscular 
nerve-branchings,  so  as  to  disable  it.  He  sees  in  this 
a  proof  that  the  nerves  which  spread  through  the  muscle 
do  not  share  in  this  form  of  irritation.  He  has,  more- 
over, discovered  that  the  nerves  are  not  equally  dis- 
tributed throughout  the  sartorius.  They  enter  at  a 
point  somewhat  below  the  middle  of  the  muscle,  and 
distribute  themselves  upward  and  downward  between 
the  muscle-fibres ;  but  they  cannot  be  traced  to  the 
ends  of  the  muscle,  and  there  are  at  these  ends  regions 
of  from  2  to  3  m.  in  length,  in  which  at  least  the 
larger  muscle-fibres  are  wanting.  (Whether  the  nerve- 
net  which,  according  to  Gerlach,  lies  within  the  sarco- 
lemma,  extends  to  these  regions,  is  another  question 
with  which  we  have  nothing  here  to  do.)  The  specific 
muscle-irritants  affect  these  regions  exactly  as  they  do 
the  rest  of  the  muscle ;  while  the  specific  nerve-irritants 
(concentrated  lactic  acid  and  glycerine)  are  never  able 
to  affect  these  ends,  though  they  elicit  single  pulsa- 
tions in  the  parts  containing  nerves.  These  nerve- 
containing  parts  are  also  more  electrically  excitable  than 
are  the  ends ;  by  curare  and  by  anelectrotonus  their 
excitability  is  decreased,  though  that  of  the  nerveless 
ends  remains  unaltered. 

Many  objections  have  been  brought  forward  against 
these  conclusions.  For  my  part,  in  the  very  insignifi- 
cance of  the  differences  between  nerve  and  muscle  in 
this  point  also,  I  am  inclined  to  see  new  reason  to 
believe  that  these  two  organs,  so  similar  in  all  points 
(as  yet  we  know  only  two  important  differences,  which 


THEORY    OF   XERVE-ACTIVITY.  259 

are,  that  the  muscle  is  contractile,  which  the  nerve  is 
not,  and  that  electrotonus,  which  intervenes  in  nerve, 
cannot  be  shown  in  muscle),  may  also  be  entirely  simi- 
lar in  the  matter  of  irritability,  and  that  those  who  dis- 
pute this  quality  are  forced  to  assume  the  existence  of 
a  substance  intermediate  between  that  of  the  nerve 
and  of  the  muscle,  and  which  diifers  almost  more  from 
the  nerve  than  from  the  muscle. 

8.  Summing  up,  it  appears  that  the  independent 
irritability  of  muscle-substance  has  not  been  proved  ; 
nor  has  it  been  disproved.  To  understand  how  the 
nerve  acts  on  the  muscle  one  must  assume  that  the 
latter  is  irritated  by  the  former,  and  therefore  there  is 
no  sufficient  reason,  remembering  the  similarity  in  all 
other  points  between  nerve  and  muscle,  to  dispute  that 
it  may  also  be  ii'ritated  by  other  irritants  (electric, 
chemical,  mechanical,  or  thermic).  In  the  theory  above 
explained  as  to  the  nature  of  the  influence  on  the 
muscle,  we  have  assumed  that  this  irritation  takes 
place  electrically.  We  have  therefore  tacitly  presup- 
posed that  the  muscle  is  electrically  excitable.  Except 
on  this  assumption,  all  that  can  be  said  is  that  the 
molecular  process  originating  in  the  nerve  is  trans- 
ferred to  the  muscle :  which  explains  nothing,  but  rather 
renounces  all  explanation.  Our  hypothesis,  on  the  other 
hand,  has  the  undeniable  advantage  that  it  is  based 
on  the  well-known  process  of  the  negative  variation  of 
the  nerve  during  its  activity.  That  the  negative  varia- 
tion, when  it  has  once  originated  in  the  nerve,  propa- 
gates itself  to  the  nerve-ends,  can  only  be  regarded  as 
natural,  and,  pro\dded  that  it  is  of  sufficient  strength, 
it  can  then  act  as  an  ii-ritant  on  the  muscle. 

We   Lave   already  seen   that   the   nerve  must   be 


260  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

regarded  as  composed  of  many  particles  arranged  one 
behind  the  other,  each  of  which  is  retained  in  a  defi- 
nite position  by  its  own  forces  and  by  the  influence 
of  the  neighbouring  particles.  Whatever  acts  as  an 
irritant  on  the  nerves  must  displace  these  particles 
from  this  position,  and  must  cause  a  disturbance,  which 
then  propagates  itself,  owing  to  the  fact  that  a  change 
in  the  position  -of  one  particle  causes  a  disturbance  in 
the  equilibrium  of  the  adjacent  particles,  in  consequence 
of  which  the  latter  are  set  in  motion.  Negative  varia- 
tion must  be  regarded  as  a  result  of  this  movement  of 
the  nerve-particles,  in  that  the  electrically  acting  parts 
are  arranged  in  different  order  by  the  movement,  and 
therefore  must  exercise  a  different  external  influence. 
But  just  as  this  change  in  the  position  of  the  nerve- 
particles  is  able  to  set  the  needle  of  a  multiplier,  if  it 
is  properly  connected  with  the  nerve,  in  motion,  so  the 
electric  process  originating  in  the  nerve  must  act  on 
the  muscle,  if  the  latter  is  sensitive  to  electric  varia- 
tions. This  was  the  assumption  from  which  we  started, 
and  which,  after  the  above  explanations,  will  be  regarded 
as  thoroughly  trustworthy.  To  enter  further  into  the 
details  of  the  activity  of  nerves  and  muscles,  and  to 
substitute  more  definite  conceptions  for  such  as  are  at 
present  often  indefinite,  is  impossible  in  the  present 
state  of  knowledfife. 


CHAPTER   XVI. 

1.  Various  kinds  of  nerves;  2.  Absence  of  indicable  differences 
in  the  fibres ;  3.  Cliaracters  of  nerve-cells  ;  4.  Various  kinds  of 
nerve-cells ;  5.  Voluntary  and  automatic  motion ;  6.  Eeflex 
motion  and  co-relative  sensation  ;  7.  Sensation  and  conscious- 
ness ;  8.  Retardation  ;  9.  Specific  energies  of  nerve-cells ;  10. 
Conclusion. 

1.  At  present  we  have  paid  attention  only  to  such 
nerve-cells  as  are  in  connection  Tvith  muscles,  and  bj 
the  activity  of  which  the  appropriate  muscles  are  ren- 
dered active.  We  have  referred  only  incidentally  to 
other  kinds  of  nerves.  The  difficulty  due  to  the  cir- 
cumstance that  a  suitable  reagent  is  necessary  for  the 
study  of  such  nerve-activity  as  does  not  express  itself 
in  any  visible  change  in  the  nerve,  compelled  us  to  con- 
fine our  studies  in  the  first  place  to  muscle-nerves  or 
'motor  nerves,  in  which  the  muscle  itself  acts  as  the 
required  reagent.  We  now  have  to  discover  how  far 
the  experiences  which  we  have  gained  of  motor-nerves, 
and  the  views  which  we  have  based  on  these  experiences, 
are  applicable  to  other  nerves. 

Besides  the  real  motor  nerves,  we  may  distinguish 
those  which  act  on  the  smooth  muscle-fibres  of  the 
blood-vessels,  through  these  effecting  a  decrease  in  the 
diameter  of  the  smaller  vessels,  and  thus  regulating  the 
circulation  of  the  blood.  These  are  called  vaso-motor 
nerves.      They  are,  however,  in  no  way  different  from 


262  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

other  motor  nerves.  "But  a  difference  is  observable 
even  in  the  case  of  the  secretory  nerves  or  gland-nerves, 
of  which  we  have  already  had  occasion  to  make  mention. 
When  these  nerves  are  irritated  the  appropriate  nerves 
begin  to  secrete.  The  connection  of  these  nerves  with 
the  glands  must  from  a  physiological  point  of  view  be 
entirely  similar  to  that  of  the  motor  nerves  with  the 
muscles.  When  the  latter  are  irritated  the  muscles 
connected  with  them  at  once  pass  into  a  state  of  activity. 
Just  in  the  same  way  the  gland-nerves,  when  they  are 
irritated,  cause  the  glands  connected  with  them  to  pass 
into  a  state  of  activity.  That  this  activity  is  quite 
different  from  that  of  the  muscles,  is  obviously  due  to 
the  entirely  different  structure  of  the  glands  and  the 
muscles.  A  gland,  unlike  a  muscle,  cannot  contract; 
when  it  become.s  active,  it  secretes  a  liquid,  this  being 
its  activity.  There  is  therefore  no  reason  to  assume 
any  difference  in  any  of  these  nerves,  the  difference  in 
the  terminal  apparatus,  in  which  the  nerves  end,  being 
sufficient  fully  to  explain  the  difference  in  the  pheno- 
mena. 

But  there  are  other  nerves  the  action  of  which  is 
much  harder  to  understand.  Among  these  are  the 
sensory  nerves.  When  these  are  irritated,  they  effect 
sensations  of  different  kinds,  some  being  of  light,  others 
of  sound,  and  so  on.  Moreover  these  nerves  are  capable 
of  receiving  irritation  in  a  peculiar  way,  some  by  waves 
of  light,  others  by  sound  vibrations,  and  others  again 
by  heat-rays ;  but  in  all  cases,  only  when  these  influ- 
ences act  on  the  ends  of  the  respective  nerves.  It  is 
not  self-evident  that  these  nerves  are  homogeneous 
in  themselves  or  with  the  previously  mentioned  kinds. 
Finally,  it  is  yet  harder  to  understand  the  action  of 


SIMILARITY    OF   NERVE-FIBRES.  263 

another,  and  the  last  class  of  nerves,  which  are  called 
retardatory  nerves  (Hemmungs-nerven).  It  is  com- 
mon knowledge  that  the  heart  beats  ceaselessly  during 
life.  Now,  if  a  certain  nerve  which  enters  the  heart 
is  irritated  the  heart  ceases  to  beat,  recommencing 
when  the  irritation  of  the  nerve  is  discontinued.  This 
remarkable  fact  was  discovered  by  Edward  Weber,  who 
spoke  of  the  phenomenon  as  retardation.  It  is  curious 
that  a  nerve  can  by  its  activity  still  a  muscle  which 
is  in  motion. 

2.  Before  we  endeavour  to  determine  this  and  the 
other  points  raised,  we  must  note  whether  any  differ- 
ences can  be  shown  in  these  various  nerves,  which  act 
in  such  entirely  different  ways.  In  the  previous  chap- 
ters we  have  observed  so  many  peculiarities  in  nerves, 
and  among  these,  qualities  which  can  be  examined 
without  the  intervention  of  the  muscle,  that  it  seems 
not  altogether  unjustifiable  to  hope  that  we  may  be 
able  to  observe  differences  also  in  nerves  if  any  such 
occur.  But  if  this  is  impossible,  if  all  nerve-fibres, 
though  examined  in  every  possible  way,  seem  to  be 
quite  homogeneous,  then  we  shall  be  justified  in  con- 
sidering them  really  homogeneous,  and  must  look  for 
an  explanation  of  the  variety  in  their  actions  in  other 
circumstances. 

It  may  at  once  be  said  that  it  is  quite  impossible 
to  show  differences  in  the  different  kinds  of  nerves. 
Microscopic  observation  shows  no  differences ;  for  the 
difference,  to  which  allusion  has  already  been  made, 
between  medullary  and  medulla-less  fibres  does  not 
affect  the  point  in  question.  We  are  obliged  to  infer 
that  the  medullary  sheath  is  of  entirely  subordinate 
significance  in  the  activity  of  the  nerve.     At  any  rate, 


264     PHYSIOLOGY  OV   MUSCLES  AND  NERVES. 

the  presence  or  absence  of  this  medullary  sheath  does 
not  correspond  with  differences  in  the  physiological 
actions  of  nerves.  Nor  are  the  small  differences  in 
diameter  of  the  separate  nerve-fibres  of  greater  import- 
ance. Nor  do  experimental  tests  bring  any  differences 
to  light.  The  bearing  of  nerves  to  irritants  does  not 
vary:  the  electromotive  effects  are  the  same  in  all.  In 
all  these  points  we  need  simply  refer  to  the  previous 
chapter,  for  the  explanations  there  given  are  equally 
true  of  all  kinds  of  nerve-fibres. 

If,  therefore,  all  kinds  of  nerve-fibres  are  alike,  we 
can  only  explain  the  difference  in  their  action  as  due 
to  their  connection  with  terminal  organs  of  various 
form.  We  have  already  made  use  of  this  principle 
in  explanation  of  the  difference  between  motor  and 
secretory  nerves,  and  we  must  now  endeavour  to  ex- 
tend it  to  all  other  nerves. 

3.  While  the  motor  and  secretory  nerves  have  their 
terminal  organs  in  the  periphery  of  the  body,  the  sensi- 
tive or  sensory  nerves  act  on  apparatus  which  are  situ- 
ated in  the  central  organs  of  the  nervous  system.  An 
irritant  which  affects  a  motor  nerve,  to  become  appa- 
rent, must  propagate  itself  toward  the  periphery,  till  it 
reaches  the  muscle  situated  there ;  an  irritant,  on  the 
other  hand,  which  affects  a  sensory  nerve,  must  be  pro- 
pagated toward  the  centre  before  it  sets  free  any  action. 
Nerves  of  the  former  kind  are  therefore  called  ceMtrlfu- 
gal,  those  of  the  latter  centrijpetal.  We  have,  however, 
already  found  that  this  does  not  depend  on  a  difference 
in  the  nerve  itself,  but  that  each  nerve-fibre,  when  it  is 
affected  at  any  point  in  its  course,  transmits  the  ex- 
citement in  both  directions  ;  and  we  therefore  presumed 
that  the  fact  that  action  takes  place  only  at  one  end 


CAPACITIES   OF   JMEEVE-CELLS.  265 

must  be  due  to  the  nature  of  the  attacbment  of  the 
fibres  to  the  terminal  apparatus.  {Cf.  chap.  xiii.  §  3, 
p.  217.) 

After  we  had  carefully  examined  the  peripheric  ter- 
minal apparatus  of  the  motor  nerves,  that  is  to  say,  the 
muscles,  we  were  in  a  position  to  study  the  processes 
in  motor  fibre.  In  order  now  to  understand  the  action 
of  sensory  fibres,  it  will  be  therefore  necessary  first 
to  obtain  further  knowledge  of  the  central  nervous 
organs. 

The  central  organs  of  the  nervous  system,  in  ad- 
dition to  nerve-fibres,  include,  as  we  have  seen  (chap, 
vii.  §  1,  p.  105  et  seq.),  also  cellular  structures,  called 
ganglion-cells,  nerve-cells,  or  ganglion-halls.  They 
are  not  always  globular,  but  are  generally  irregular  in 
form.  Beside  the  forms  represented  in  fig.  27  (p.  106), 
which  occur  scattered  here  and  there  in  the  course  of 
the  peripheric  nerves,  forms  such  as  those  represented  in 
fig.  68  occur  much  more  abundantly  in  the  central  or- 
gans. They  generally  have  many  processes  (four,  six  and 
even  up  to  twenty),  which  branch  and  unite  together 
like  network.  Many  cells  exhibit  one  process,  difi'er- 
ing  from  the  others,  which  passes  into  a  nerve-fibre 
(nerve-process :  cf.  fig.  68,,  la  and  3c).  These  nerve- 
processes  pass  out  from  the  central  organ  and  form 
the  peripheric  nerves.  Within  the  central  organ  the 
processes  of  the  ganglion-cells  form  a  very  involved 
network  of  fibres  ;  between  these  there  are,  however, 
other  fibres  which  completely  resemble  the  peripheric 
nerve-fibres.  There  is  no  reason  for  ascribing  to  these 
fibres  of  the  central  organ  qualities  other  than  those  of 
the  peripheric  fibres.  When  in  the  central  organ  phe- 
nomena are  observed  which  never  occur  in  the  peri- 


266 


PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 


pheric  nerve-tibres,  it  is  natural  to  refer  these  to  the 
presence  of  the  ganglion-cells. 

As  a  matter  of  fact,  all  organs  which  contain  nerve- 
cells,    the   central    organs    as   well  as  the    peripheric 


Fig.  68.    Ganglion-cells  from  the  human  brain. 

1.  A  eaiigUon-cell,  of  which  one  process,,  a,  becomes  the  axis-cj'linder  of  a  nerve- 
fibre,  6.  2.  Two  cells,  a  and  b,  interconnected.  3.  Diagrammatic  representa- 
tion of  three  connected  cells,  each  of  -which  passes  into  a  nerve-fibre,  c.  4. 
Ganglion-cell  partly  filled  ^^•ith  black  pigment. 

organs,  in  which  they  are  present,  though  not  so  abun- 
dantly, exhibit  certain  peculiarities,  which  we  must  re- 
gard as  caused  by  the  nerve-cells,  /.nd  as  we  are  in  no 
case  able  to  examine  the  nerve-cell  by  itself,  but  must 
always  examine  it  in  connection  with,  and  mingled  with 
the  nerve-fibres,  we  can  but  carefully  determine  the  dif- 


CAPACITIES    OF   NERVE-CELLS.  267 

ference  in  the  behaviour  of  these  organs  from  that  of 
ordinary  nerve-fibres,  and  then  regard  all  not  appertain- 
ing to  the  nerve-fibres  as  peculiar  to  the  nerve-cells. 

We  know  that  the  nerve-cells  are  irritable,  that 
thej  transmit  the  excitement  which  arises  in  them,  and 
transfer  it  at  the  terminal  orofan.  The  excitement  can 
never  occur  of  itself  in  a  nerve-fibre,  but  it  always  re- 
sults from  an  irritant  acting  externally,  and  can  never 
pass  from  one  nerve-fibre  to  another,  but  always  remains 
isolated  in  the  excited  fibre. 

But  where  nerve-cells  occur,  the  case  is  different. 
As  long  as  a  nerve-fibre  passes  uninjured  from  the  brain 
and  spinal-marrow,  or  from  one  of  the  accumulations  of 
nerve-cells  situated  in  the  periphery,  to  a  muscle,  ex- 
citement arises  without  externally  visible  cause,  and 
this  acts  through  the  nerve  on  the  muscle,  sometimes  at 
regular  intervals  independently  of  the  will,  sometimes 
from  time  to  time  at  the  instigation  of  the  will.  Again, 
where  nerve-cells  occur,  we  find  that  excitements  which 
are  transmitted  to  the  central  organ  by  a  nerve-fibre 
may  there  be  imparted  to  other  nerve-fibres.  Thirdly, 
we  find  that  excitements  which  are  transmitted  to  the 
central  organ  by  nerve-fibres  there  elicit  a  peculiar 
process,  which  is  called  sensation  and  consciousness. 
Fourthly  and  finally,  the  remarkable  phenomenon, 
mentioned  above,  of  retardation,  only  occiu-s  where 
nerve-cells  are  present.  The  four  following  qualities, 
which  are  entirely  absent  in  nerve-fibres,  must  there- 
fore be  attributed  to  nerve-cells : — 

(1)  Excitement  Tnay  arise  in  them  independently, 
i.e.  luithout  any  visible  external  irritant. 

(2)  They  are  able  to  transfer  the  excitement  from 
one  fibre  to  another. 


268  THYSIOLOGY    OF   MUSCLES   AIS'D   NERVES. 

(3)  They  can  receive  an  excitement  transmitted  to 
them  and  transmute  it  into  conscious  sensation. 

(4)  They  are  able  to  cause  the  suppression  (retar- 
dation) of  an  existing  excitement. 

4.  From  the  above  it  must  not  be  supposed  that  all 
ganglion-cells  possess  all  these  qualities.  On  the  con- 
trary, it  is  to  be  supposed  that  each  nerve-cell  per- 
forms but  one  of  these  functions,  and  .even  that  there 
are  more  minute  differences  in  them,  so  that,  for  in- 
stance, the  nerve-cells  which  accomplish  sensation  are 
of  various  kinds,  each  of  which  accomplishes  but  one 
distinct  kind  of  sensation.  This  is  no  mere  hypo- 
thesis, for  there  are  established  facts  which  confirm 
the  view.  Conscious  sensations  occur  only  in  the  brain, 
and  the  various  parts  of  the  brain  may  be  separately 
removed  or  disabled,  in  which  case  individual  forms 
of  sensation  fail,  while  others  remain  undisturbed. 
If  the  whole  brain  is  removed,  the  nerve-cells  of  the 
dorsal  marrow  suffice  fully  to  accomplish  the  pheno- 
mena of  the  transference  of  excitement  from  one  nerve- 
fibre  to  another.  Again,  there  are  certain  regions  of 
the  brain  which  separately  are  able  to  give  rise  to  inde- 
pendent excitement  in  themselves ;  and  certain  accumu- 
lations of  nerve-cells  which  lie  outside  the  actual  central 
nervous  organs  have  the  same  power.  The  forms  which 
nerve-cells  assiune  being  very  varied,  it  often  happens 
that  the  cells  of  certain  regions,  where  only  certain  capa- 
bilities can  be  shown,  are  alike  in  form,  and  differ  in  this 
respect  from  the  cells  of  other  regions,  where  the  capa- 
bilities are  different.  As  yet,  however,  it  has  not  been 
found  possible  to  distinguish  differences  in  form  suffi- 
ciently characteristic,  and  relations  between  the  form  and 
the  function  of  nerve-cells  sufficiently  characteristic  to 


FORMS   OF   NERVE-CELLS.  269 

make  it  possible  definitely  to  infer  the  function  of  a  cell 
from  its  form.  On  the  contrary,  it  is  better,  by  experi- 
ments with  animals  and  experiences  with  invalids,  to 
determine  step  by  step  what  functions  belong  to  the 
cells  of  a  given  region.  Considering  the  complex  and 
yet  very  imperfectly  known  structure  of  the  central 
nervous  organs,  it  is  not  svu'prising  that  this  task  has 
by  no  means  yet  been  fully  accomphshed.  As  in  the 
present  work  we  are  not  treating  of  the  physiology  of 
the  separate  parts  of  the  nervous  system,  but  are  only 
concerned  with  the  general  characters  of  the  elements 
which  constitute  the  nervous  system,  we  must  not 
enter  into  details ;  but  we  must  be  satisfied  to  show 
what  the  nerve-cells  in  general  are  able  to  accomplish 
and  to  give  due  prominence  to  the  fact  that  each 
separate  nerve-cell  is  probably  always  able  to  accom- 
plish only  one  definite  thing.  We  will  now  run 
through  these  capacities  and  show  the  facts  which 
serve  as  proof  of  these. 

5.  The  natural  rise  of  excitement  takes  place 
either  voluntarily  or  involuntarily.  We  are  always 
able  voluntarily  to  contract  our  muscles,  though  not 
all  of  these,  for  many,  especially  the  smooth  forms, 
are  not  subject  to  the  will,  but  contract  only  as  the 
result  of  other  causes.  Sometimes,  moreover,  the  want 
of  power  to  contract  certain  muscles  is  to  be  ascribed 
only  to  want  of  use,  as  is  shown  by  the  fact  that 
some  men  are  able  voluntarily  to  contract  the  skin 
of  their  scalps  or  their  ear-muscles,  though  this  is 
impossible  to  most  men,  or  is  possible  only  in  a 
very  restricted  degree.  Similarly,  it  is  a  matter  of 
use  how  far  the  will  is  able  to  effect  a  limited  con- 
traction   of   separate   muscles  or    parts    of  a    muscle. 


270  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

Those  beginning  to  play  the  piano  find  it  difficult  to 
move  individual  fingers  apart  from  the  others,  though 
by  practice  they  soon  learn  to  do  this.  \Yhenever 
an  intended  contraction  of  a  muscle  is  accompanied 
by  another  unintended  and  simultaneous,  the  latter 
is  called  a  co-relative  movetnent.  Such  co-relative 
movements  sometimes  accompany  illness.  Stammerers, 
for  instance,  when  they  speak,  twitch  the  face  muscles 
or  even  those  of  the  arm.  It  has  also  been  observed 
that  in  the  case  of  injuries,  after  blood  has  been  lost 
from  the  brain,  movements  of  the  injured  limbs  not 
voluntarily  possible  occur  involuntarily  as  co-relative 
motions.  Some  co-relative  movements  are  natural  in 
the  organism ;  for  instance,  when  the  eye  is  turned 
inward,  the  pupil  simultaneously  decreases  in  size,  and 
a  contraction  of  the  adjusting  muscle  occurs,  by  which 
the  eye  is  enabled  to  see  at  a  short  distance.  This 
co-relative  motion  has  been  regarded  as  a  case  of  the 
transmission  of  the  excitement  from  one  nerve- fibre  to 
another;  but  it  seems  to  me  that  this  is  incorrect. 
For  there  is  nothing  to  show  that  the  excitement 
originated  in  one  fibre  and  was  then  transferred  to 
other  fibres,  and  it  is  more  simple  to  assume  that  the 
various  fibres  were  excited  simultaneously  by  the  will, 
either  because  isolated  excitement  of  these  fibres  sepa- 
rately is  really  impossible  on  account  of  the  anatomical 
structure  of  the  nerve,  or  because  of  an  insufficient 
specialisation  of  the  influence  of  the  will,  resulting 
from  want  of  exercise — that  is,  it  is  due  to  unskilful- 
ness  on  the  part  of  the  will. 

If  it  is  asked  how  the  voluntary  excitement  of  the 
nerve-fibres  is  caused  in  the  nerve-cells,  an  answer 
is  yet  to  be  sought  in  physiology.     Into  the  question 


VOLUNTARY  AND  AUTOMATIC  MOVEMENTS.    271 

wliether  there  is  actually  a  purely  voluntary  excite- 
ment, that  is,  that  no  incitement  acted  externally 
on  the  brain  but  that  the  excitement  originated  quite 
spontaneously,  we  will  not  enter  further  here.  All 
that  is  certain  is  that  in  many  cases  an  action  appears 
to  be  voluntary  which,  if  the  process  is  more  closely 
analysed,  is  found  to  result  from  external  influences. 
But  the  physiological  process  by  which  (whether 
externally  influenced  or  not)  excitement  arises  in 
the  nerve-cells,  which  excitement  is  then  transmitted 
through  the  nerve-fibre  to  the  muscle,  is  as  yet  ex- 
tremely obscure ;  and  if  it  is  said  that  it  is  a  molecular 
motion  of  the  constituent  particles  of  the  nerve-cell, 
this  explains  nothing,  but  merely  expresses  the  convic- 
tion that  it  is  not  a  supernatural  phenomenon,  but 
merely  a  physical  process  analogous  to  the  process  of 
excitement  in  the  peripheric  nerves. 

Involuntary  movements  occur  sometimes  irregularly, 
as  twitchings,  spasms ;  sometimes  regularly,  as  in  the 
case  of  respiratory  movements,  the  movements  of  the 
heart,  the  couti'actions  of  the  vascular  muscles,  of  the 
intestinal  muscles,  and  so  on.  The  latter,  which  occur 
with  more  or  less  regularity  while  life  lasts,  and  are 
for  the  most  part  of  deep  significance  as  regards  the 
normal  condition  of  the  vital  phenomena,  have  natu- 
rally been  especially  subjected  to  thorough  research. 
They  are  called  automatic  nnovements,  that  is,  they 
occur  independently  of  the  co-operation  of  the  will, 
and  apparently  without  any  incentive.  But  notwith- 
standing this,  it  is  chiefly  in  such  cases  that  the  causes 
which  effect  the  excitement  of  the  nerves  concerned 
have  been  to  a  certain  extent  established. 

Automatic  movements  may  be   distinguished  into 


272  THYSIOLOGY    OF   MUSCLES   AND   NERVES. 

such  as  are  rhythinic,  in  which  contraction  and  relaxa- 
tion of  the  muscles  concerned  take  place  in  regular 
alternation,  as  in  respiration  and  in  the  movements  of 
the  heart ;  such  as  are  tonic,  in  which  the  contractions 
are  more  constantly  enduring,  even  if  the  degree  of 
contraction  varies,  as  in  the  contraction  of  the  vascular 
muscles,  and  of  the  rainbow  membrane  of  the  eye ;  and 
such  as  are  irregular,  i.e.  the  peristaltic  movements  of 
the  intestine.  Our  knowledge  of  automatic  movements 
is  based  principally  on  those  connected  with  respira- 
tion ;  but  the  conceptions  gained  in  this  case  may  be 
directly  applied  to  the  other  cases.  It  will  be  suffi- 
cient therefore  to  speak  of  respiratory  motion  only. 

Eespiration  begins  immediately  after  birth,  and 
its  movements  continue  from  that  time  throughout  life. 
In  the  higher  animals  (mammals  and  birds)  they  are 
unconditionally  necessary  for  the  preservation  of  life, 
for  only  by  their  means  is  sufficient  oxygen  conveyed 
to  the  blood  to  provide  for  all  the  vital  processes.  On 
the  other  hand,  when  the  organ  from  which  the  ex- 
citement of  the  respiratory  muscles  proceeds  is  in 
any  way  insufficiently  nourished  or  is  otherwise  in- 
jured in  condition,  respiratory  action  ceases  and  life  is 
threatened.  This  organ  is  a  limited  point  in  the 
Tnedulla  oblongata,  formed  of  a  mass  of  nerve-cells,  in 
which  the  excitements  originate,  and  from  which  they 
are  conveyed  by  the  nerves  to  the  respiratory  muscles. 
This  is  called  the  respiratory  centre  {Lehenshnoten 
of  the  Grermans,  noeud  vital  of  the  French),  because 
of  its  importance  to  life.  It  is  the  spot  which  the 
matador  in  bull-fights  must  reach  by  a  skilful  blow 
with  his  knife,  to  bring  the  enraged  animal  to  the 
ground  ;  it  is  the  spot  which,  if  crushed  between  the 


VOLUNTARY    AND    AUTOMATIC    MOVEMENTS.  273 

first  and  second  vertebrae,  the  result  is  instant  death 
by  the  so-called  dislocation  of  the  neck.  It  has  been 
shown  that  the  cause  which  induces  this  ceaseless 
activity  in  the  nerve-cells  of  the  respiratory  centre 
lies  in  the  character  of  the  blood.  When  the  blood 
is  quite  saturated  with  oxygen,  then  the  activity  of 
the  respiratory  centre  commences.^  When  the  blood 
becomes  freer  from  oxygen,  the  respiratory  motions 
become  stronger. 

Far  from  being  necessarily  active,  independently  and 
without  external  incentive,  the  nerve-cells  of  the  respi- 
ratory centre  are  also  rendered  active  by  external  cir- 
cumstances. But  they  are  much  more  sensitive  than  the 
nerve-fibres,  so  that  they  are  influenced  even  by  slight 
changes  in  the  gaseous  contents  of  the  blood  which 
plays  over  them.  And  the  other  automatic  nerve-cells 
behave  exactly  as  do  the  cells  of  the  respiratory  centre. 
Yet  small  differences  in  sensitiveness  occur  among 
them,  so  that  some  are  excited  even  when  only  the 
average  amount  of  oxygen  is  contained  in  the  blood, 
others  when  a  point  lower  than  this  average  has  been 
reached,  as  happens  only  occasionally  during  life. 

It  would  take  too  long  to  apjDly  this  theory,  now 

•  Experimental  proof  of  this  may  alwa3's  be  tried  by  anyone 
on  himself.  Attention  must  be  given  for  a  time  to  the  respiratory 
movements,  their  depth  and  number  being  noted.  From  eight 
to  ten  inspirations  and  expirations  are  then  drawn  slowly  one 
after  the  other.  By  this  means  much  more  air  is  introduced  into 
the  lungs  than  by  ordinarj'  respiration,  and  the  blood  can  therefore 
thoroughly  saturate  itself  with  ox3'gen.  If,  after  this,  voluntary 
respiration  is  ceased,  it  will  be  found  that  twenty  seconds  or  more 
elapse  before  a  respiration  again  occurs,  long  enough  that  is  for  the 
consumption  of  the  introduced  oxygen.  Only  after  this  do  respira- 
tions begin,  at  first  weakly,  but  always  increasing  in  strength,  until 
the  former  regular  respiration  again  prevails. 
13 


274  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

briefly  explained,  to  each  of  the  other  processes  of 
automatic  motion.  We  must  content  ourselves  with 
the  remark  that  an  analogous  conception  of  the  nature 
of  the  movements  of  the  heart  is  probable,  though  no 
experimental  proof  of  its  correctness  has  yet  been 
achieved.  The  cause  of  movements  of  the  intestine  is 
not  quite  so  difficult  to  understand ;  at  any  rate,  the 
main  principles  found  in  the  case  of  the  nerve-cells  of 
the  respiratory  centre  are  valid  in  the  case  of  all  other 
automatic  centres.^  Mention  must  still  be  made  of 
the  fact  that  in  the  heart  and  intestine  the  nerve-cells 
from  which  the  automatic  action  proceeds  are  situated 
within  the  respective  organs  themselves.  For  this 
reason  these  organs  can  yet  exhibit  movements  after 
the  nerve-centres  have  been  destroyed,  or  the  organs 
have  been  cut  from  the  body. 

6.  The  transference,  by  means  of  the  nerve-cells, 
of  an  excitement  from  one  nerve-fibre  to  another  is 
most  clearly  shown  in  that  which  is  called  reflec- 
tion. By  this  term  is  meant  the  passage  of  an  excite- 
ment, which  having  acted  on  a  sensory  fibre  has  been 
transmitted  by  it  to  the  nerve-cells,  to  a  centrifugal 
fibre,  by  which  it  is  conducted  back  from  the  centre 
(as  a  ray  of  light  is  reflected  from  a  mirror)  and 
makes  its  appearance  at  another  point.  The  reflection 
can  occur  either  in  a  m,otor  fihre,  in  which  case  it  is 
called  a  reflex  action,  or  in  a  secretory  or  retarda- 
tory  fibre.  The.  former  case  is  more  common  and 
better  known.  As  examples  of  such  reflex  actions,  I 
may  mention  the  closing  of  the  eyelids  on  the  irrita- 

'  Those  who  wish  to  obtain  further  information  as  to  these  cir- 
cumstances may  be  referred  to  my  work  BemerTiimgen  iiier  die 
Thdtigheit  dcr  autoviatischen  A^erven-centra,  &c.     Erlangen,  1875. 


REFLEX    MOTIONS.  ^  275 

tion  of  the  sensory  nerves  of  the  eye,  sneezing  on 
irritation  of  the  mucous  membrane  of  the  nose,  cough- 
ing on  the  irritation  of  the  mucous  membrane  of  the 
respiratory  organ.  Wherever  sensory  nerves  are  con- 
nected by  nerve-cells  with  motor  nerves,  these  reflex 
actions  may  occur.  If  an  animal  is  decapitated  and 
its  toe  is  pinched,  the  leg  is  drawn  up  and  contractions 
occur  in  it.  The  reflex  actions  are  here  accomplished 
through  the  nerve-cells  of  the  spinal  marrow,  and  the 
removal  of  the  brain  favours  the  action,  while  it  at  the 
same  time  excludes  the  possibility  of  the  intervention 
of  voluntary  movements. 

There  is  no  doubt  that  in  this  process  the  nerve- 
cells  play  a  part,  and  that  the  process  does  not  depend 
solely  on  the  direct  transference  of  the  excitement  from 
a  sensory  nerve-fibre  to  an  adjacent  motor  nerve-fibre. 
Apart  from  the  fact  that  the  transference  never  takes 
place  except  where  nerve-cells  can  be  shown  to  be  pre- 
sent, this  is  confirmed  by  the  fact  that  the  process  of 
reflex  transference  occupies  a  very  noticeable  time, 
much  longer  than  that  required  for  transmission 
through  the  nerve-fibres.  With  the  knowledge  which 
we  have  now  gained  of  the  structm'e  of  the  central 
nervous  organs,  it  may  be  considered  established,  that 
nowhere  is  there  immediate  connection  between  sen- 
sory and  motor  nerve-fibres,  but  a  mediate  connection 
through  the  nerve-cells.  This  allows  the  possibility  of 
the  propagation  of  an  excitement  from  a  sensory  nerve- 
fibre,  through  a  nerve-cell,  to  a  motor  nerve-fibre.  It 
is  thus  intelligible  how,  owing  to  the  interconnec- 
tion of  the  nerve-cells,  the  passage  of  the  excitement 
from  any  sensory  nerve-fibre  to  any  or  every  motor 
nerve-fibre   is   possible,   for  the  excitement  advances 


276  PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 

from  nerve-cell  to  nerve-cell,  from  each  of  which  it 
can  repass  into  a  motor  fibre.  From  the  length  of 
the  time  occnpied  by  the  reflex  irritant,  it  is  to  be 
inferred  that  the  transmission  of  the  excitement  has 
to  meet  considerable  resistance  in  the  nerve-cells. 
This  resistance  naturally  increases  with  the  number  of 
nerve-cells  to  be  traversed,  so  that  the  transference  of 
a  reflex  action  from  a  definite  sensory  fibre  to  different 
motor  nerve-fibres  is  not  always  equally  difficult,  and 
is  the  more  difficult  the  greater  is  the  number  of 
the  cells  which  lie  between  the  two.  All  this  agrees 
with  the  facts  found  by  experiment.  It  also  explains 
why,  by  certain  influences,  not  only  is  the  reflex  trans- 
ference rendered  easier,  but  the  passage  of  the  excite- 
ment to  the  most  remote  motor  fibres  is  also  rendered 
peculiarly  possible.  The  best  known  case  of  this  is 
poisoning  by  strychnine.  This  so  greatly  facilitates  the 
reflex  transference  that  the  slightest  touch  on  any  point 
of  the  skin,  or  even  the  disturbance  caused  by  a  breath, 
is  sufficient  to  throw  all  the  muscles  of  the  body  into 
violent  reflex  tetanus. 

As  each  excitement  of  a  sensory  fibre  which  reaches 
the  nerve-centre  can  give  rise  to  a  conscious  sensation, 
the  spread  of  the  excitement  within  the  centre  must 
have  the  same  effect  as  would  be  the  case  if  a  larger 
number  of  excitements  of  several  sensory  fibres  reached 
the  centre  simultaneously.  This  process,  vvhich,  how- 
ever, only  occurs  in  the  case  of  strong  excitements, 
is  called  co-relative  sensation.  Sensation  is  caused 
not  only  by  the  excitement  of  the  nerve-cell  directly 
concerned,  but  also  by  the  spread  of  the  excitement 
to  the  other  nerve-cells.  It  may  also  be  spoken  of  as 
the  radiation  of  the  sensory  irritant,  because  the  excite- 


SENSATION   AND   CONSCIOUSNESS.  277 

ment  seems  to  spread  within  certain  limits  from  the 
point  directly  touched. 

7.  These  phenomena  will  become  more  evident 
when  we  have  more  accurately  learned  the  origin  of 
conscious  sensations  in  general,  and  the  conceptions 
which  depend  on  this.  In  order  that  such  conscious 
sensations  should  result  it  seems  absolutely  necessary 
that  the  excitement  should  reach  the  main  brain 
{cerehriiiii).  Whether  other  parts  of  the  brain,  or  even 
the  spinal  marrow,  are  able  to  give  rise  to  conscious 
sensations  is  at  least  very  doubtful,  and  is  at  any  rate 
not  proved.'  But  when  the  excitement  reaches  the 
brain,  it  gives  rise  not  only  to  feelings,  but  also  to 
very  definite  conceptions  as  to  the  nature  of  the  excite- 
ment, its  cause,  and  the  locality  at  which  it  acts.  It 
is  true  that  sometimes  this  effect  fails  and  the  irritant 
does  not  reach  consciousness,  as,  for  example,  when  the 
attention  is  strongly  attracted  in  some  other  direction, 

•  The  dispute  about  the  so-called  '  mind  in  the  spinal  marrow  ' 
(^Ruckenmarh!>scelc),t\ic  question,  that  is,  whether  more  or  less  clear 
conscious  conceptions  can  occur  in  the  nerve-cells  of  the  spinal  cord, 
was  long  and  hotlj'  debated,  but  is  now  at  rest.  It  appears  to  me 
that  the  whole  form  of  the  question  is  unscientific,  for  the  question 
can  simply  not  be  solved  with  the  means  for  research  which  we  can 
command.  Our  own  consciousness  informs  us  as  to  our  own  sensa- 
tions and  conceptions,  and  we  learn  those  of  others  from  their  lips. 
Where  this  fails,  opinion  is  always  untrustworthy,  as,  for  example, 
where  we  try  to  infer  the  feelings  of  men  from  their  behaviour. 
It  is,  however,  yet  more  hazardous  to  attach  importance  to  the 
movements  of  a  brainless  animal,  and  it  is  therefore  not  surprising 
that  two  observers  should  draw  quite  different  conclusions  from  the 
same  facts,  one  explaining  them  as  simple  reflections,  the  other  being 
of  opinion  that  such  behaviour  under  such  circumstances  is  only  ex- 
plicable as  the  result  of  conscious  sensations  and  conceptions.  The 
lower  the  animal  is  in  the  scale,  the  more  i;ntrust worthy,  naturally, 
is  the  decision. 


278  PHYSIOLOGY    OF    MUSCLES    AND    NERVES. 

or  as  in  sleep.  The  irritant  can  then  elicit  a  reflex 
action,  though  there  is  no  consciousness  of  this.  That 
the  origin  of  conscious  conceptions  is  also  an  activity 
of  the  nerves  is  certain,  and  it  is  the  cells  of  the 
grey  matter  of  the  brain  which  possess  this  activity. 
On  the  other  hand,  we  are  entirely  unable  even  to 
indicate  how  this  consciousness  comes  into  being.  It 
may  be  dae  to  molecular  processes  in  the  nerve-cells 
which  result  from  the  received  excitement ;  but  mole- 
cular processes  are  but  movements  of  the  molecules, 
and  though  we  can  understand  how  such  movements 
cause  other  movements,  we  are  entirely  unaware  how 
these  can  be  translated  into  consciousness.^ 

The  excitements  transmitted  by  the  various  sensory 
fibres  do  not  all  act  in  the  same  way  on  the  brain,  and 
the  sensations  to  which  they  give  rise  differ.  Accord- 
ingly, we  may  distinguish  the  various  sensations  of 
the  various  senses,  and  even  within  one  and  the  same 
sense  various  sub-species,  as  the  colours  in  the  sphere 
of  optical  sensations,  the  various  pitches  in  the  sphere 
of  auditory  sensations.  But  as  all  the  nerve-fibres 
which  accomplish  the  various  sensations  differ  in  no 
way  from  each  other,  we  are  forced  to  look  in  the 
nerve-cells  for  the  reason  of  the  difference  in  sensations. 
Just  as  we  assumed  that  motor  nerve-cells  differ  from 
sensory,  so  we  must  further  assume  that  among 
sensory  nerve-cells,  the  excitement  of  which  always 
elicits  the  conception  of  light,  others  again  the  excite- 

'  E.  du  Bois-Reymond  has  entered  further  into  this  question  in 
his  address  to  the  assembly  of  naturalists  at  Leipzig  ( Ueier  die 
Grenxen  des  Katurcrliennens,  Leipzig,  1872).  Some  of  the  younger 
natural  philosophers  seem  inclined  to  avoid  the  difficulty  by  ascrib- 
ing, as  does  Schopenhauer,  sensation  and  consciousness  to  all  mole- 
cules, but  this  does  not  seem  to  me  to  be  any  real  gain. 


SENSATION   AND    CONSCIOUSNESS.  279 

ment  of  which  always  elicits  the  conception  of  sound, 
others  again  the  excitement  of  which  always  results  in 
the  conception  of  taste,  and  so  on.  In  entire  accord- 
ance with  this  assumption  is  the  fact  that  it  does  not 
matter  what  external  cause  effects  the  excitement  of 
any  one  nerve-fibre,  but  that  every  excitement  of  a  given 
nerve-fibre  is  always  followed  by  a  given  sensation. 
Thus,  the  nerve  of  sight  may  be  mechanically  or  elec- 
trically irritated,  with  the  result  of  producing  a  sensa- 
tion of  light ;  mechanical  or  electric  irritation  of  the 
auditory  nerve  effects  a  sound  sensation  ;  electric  irri- 
tation of  the  nerve  of  taste  efi"ects  just  such  a  sensa- 
tion of  taste  as  does  the  influence  of  a  tasted  substance. 
It  even  happens  that  the  exciting  cause  is  situated 
in  the  brain  itself  and  directly  excites  the  nerve-cells, 
and  the  sensations  which  are  thus  elicited  are  indis- 
tinguishable from  those  which  are  effected  through 
the  nerves.  To  this  are  due  the  subjective  sensations, 
hallucinations  and  so  on,  which  depend  on  an  altera- 
tion in  the  character  of  the  blood,  or  on  an  increase 
in  the  sensitiveness  in  the  nerve-cells. 

Wherever  the  excitement  occurs,  whether  in  the 
nerve-cells  themselves  or  anywhere  in  the  course  of  the 
nerves  leading  to  the  cells,  consciousness  always  refers 
the  sensation  to  the  presence  of  some  external  cause  of 
excitement.  If  the  nerve  of  sight  is  pressed,  the 
patient  believes  that  he  sees  a  light  external  to  his 
body-^  if  a  nerve  of  touch  is  irritated  at  any  point  in 
its  course  (e.g.  the  elbow-nerve  at  the  furcation  of  the 
elbow-bones),  the  patient  feels  something  in'  the 
nerves  distributed  in  the  skin  (in  our  example  in  the 
two  last  fingers,  and  in  the  outer  edge  of  the  palm  of 
the  hand).     Our  power  of  conception  therefore  always 


280     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

projects  every  sensation  which  reaches  the  conscious- 
ness ontward,  that  is,  to  where  the  cause  of  the  excite- 
ment is  normally.  This  so-called  laiv  of  eccentric 
sensations  finds  an  easy  explanation  in  the  supposi- 
tion that  the  conception  of  the  locality  of  the  efficient 
cause  is  gained  from  experience.^  It  will  easily  be 
understood  that  this  necessarily  follows  from  the  cha- 
racters which  we  have  ascribed  to  the  nerve-cells. 
When  the  nerve-cell  is  irritated,  the  same  sensation 
and  the  same  conception  must  always  result.  Just  as  it 
makes  no  difi"erence  in  the  case  of  a  muscle  whether  the 
excitement  conveyed  to  it  by  a  motor  nerve  starts  from 
a  higher  or  from  a  lower  point  on  the  nerve,  or  whether 
the  nerve  has  been  irritated  mechanically,  electrically, 
or  by  the  will,  so  the  process  in  the  nerve-cell  does  not 
depend  on  the  locality  or  the  nature  of  the  excite- 
ment. When  the  circumstances  which  give  rise  to 
the  irritation  are  abnormal,  the  result  is  an  illusion 
of  the  senses,  that  is,  a  false  cause  is  assigned  to  a 
perfectly  clear  and  true  sensation. 

8.  The  nature  of  the  last  of  the  capabilities  which 
we  have  attributed  to  the  nerve-cells,  the  retardation 
of  a  motion,  is  still  very  obscure.  The  fact  of  retarda- 
tion is  as  yet  principally  known  in  the  case  of  auto- 
matic motion,  though  retardation  of  reflex  action  also 
occurs,  as  may  be  inferred  even  from  the  fact  that  the 
rise  of  reflex  actions  is  hindered  by  the  activity  of  the 
nerves,  especially  when  this  originates  from  the  brain. 
The  respiratory  movements  being  of  all  automatic  move- 

'  Details  of  this  matter,  into  whicli  we  cannot  enter  further 
here,  will  be  found  in  Bernstein's  The  Five  Senses  of  Man  (Inter- 
national Scientific  Series,  vol.  xxi.),  and  in  Hiixlej-'s  Elementary 
Physiology. 


RETAEDATION.  281 

ments  the  best  known,  it  is  on  these  that  the  current 
views  as  to  the  retardatory  nerves  are  based.  It  has 
been  explained  in  §  5  that  the  respiratory  movements 
result  from  the  excitement  of  the  nerve-cells  of  the  re- 
spiratory centre.  These  movements  may  be  accelerated 
or  retarded,  though  all  the  other  conditions  remain 
unchanged,  if  certain  nerve-fibres  which  pass  from  the 
mucous  membrane  of  the  air-passage  to  this  respira- 
tory centre  are  irritated.  These  retardatory  nerves 
are  distinguished  from  those  which  pass  to  the  heart 
by  the  fact  that  it  is  not  known  whether  the  latter  pass 
to  the  muscles  of  the  heart  or  to  the  nerve-cells 
situated  in  the  heart,  a  doubt  which  is  satisfied  in 
the  case  of  the  former  by  their  anatomical  arrange- 
ment. Of  the  retardatory  fibres  of  the  heart  it  might 
be  supposed  that  they  in  some  way  incapacitate  the 
muscle  from  contracting ;  in  the  case  of  the  retar- 
datory nerves  of  the  respiratory  system  such  supposi- 
tion may  be  at  once  rejected,  for  they  are  in  no  way  in 
contact  with  the  respiratory  muscles.  The  only  pos- 
sible explanation  is  therefore,  that  the  retardatory 
nerves  act  on  the  nerve-cells  in  which  the  excitement 
is  generated,  thus  either  preventing  the  excitement  from 
even  coming  into  existence,  or  preventing  the  excite- 
ment from  passing  from  the  nerve-cells  in  which  it  is 
generated  to  the  appropriate  motor  nerve-cells.  For 
various  reasons  the  latter  view  has  been  preferred.  It 
is  supposed  that  the  automatically  acting  ganglion-cells 
are  not  directly  connected  with  the  appropriate  nerve- 
fibres,  but  that  conducting  intermediate  apparatus  are 
present  between  the  two,  and  that  these  offer  a  great 
resistance.  This  explains  both  the  occurrence  of  the 
rhythmic   motions    and    the   retardation.     The    latter, 


282     PHYSIOLOGY  OF  MUSCLES  AND  NERVES. 

that   is,  is  due  to  an  increase  in   the   resistance   by 
which  the  motion  is  temporarily  suspended.' 

Eetardatory  nerves  have  been  recognised  in  almost 
all  automatic  apparatus,  and  all  are  accounted  for  by 
the  above  explanation.  The  same  explanation  may  also 
be  applied  at  once  to  the  retardation  of  reflex  action  ; 
for  even  in  the  passage  of  the  excitement  from  the 
sensory  to  the  motor  nerves  very  great  resistance  has 
to  be  overcome,  and  an  increase  in  this  resistance 
must  prevent  the  passage  of  the  excitement  and  thus 
hinder  reflex  action.  Our  acquaintance  with  this  sub- 
ject is,  however,  not  yet  by  any  means  complete,  and 
a  final  opinion  on  the  matter  is  therefore  for  the  time 
impossible. 

I  will  only  mention  further  that  the  opposite  effect, 
the  facilitation  of  the  passage  of  the  excitement  from 
the  nerve-cells  in  which  it  originates,  to  the  peripheric 
nerve-courses,  appears  to  occur. 

Finally,  it  is  sometimes  observable  that  when  those 
portions  of  the  nerves  which  contain  nerve-cells  are 
continually  and  regularly  irritated,  a  rhythmic  or  even 
an  irregular  movement  results,  instead  of  a  regular 
tetanic  contraction  of  the  muscles  concerned, — a  cir- 
cumstance which  is  evidently  to  be  explained  in  the 
same  way  as  rhythmic  automatic  activity.  The  regu- 
lar excitement  having  to  pass  through  nerve-cells  is 
modified  by  the  great  resistance  present  in  these,  and 
is  transformed  into  a  rhythmic  motion,  while  when  the 
nerve  and  the  muscle  are  directly  connected,  the  latter 
responds  to  a  continuous  excitement  of  the  nerve  with 
a  regular  and  continuous  contraction. 

o 

>  See  my  account  of  the  automatic  nerve-centres,  to  which  refer- 
ence has  already  been  made. 


SPECIFIC    ENERGIES    OF    NERVE-CELLS.  283 

9.  From  all  these  details  it  is  very  evident  that 
the  nerve-fibres  are  homogeneous  the  one  with  the 
other,  and  that  the  difference  in  their  effects  is  to  be 
referred  to  their  connection  with  nerve-cells  of  varied 
form.  This  seems,  however,  to  be  opposed  to  the  fact 
that  the  different  sense-nerves  are  irritable  by  quite 
different  influences,  and  each  of  them  only  by  quite 
definite  influences — the  nerve  of  sight  by  light,  the 
nerve  of  hearing  by  sound,  and  so  on.  It  would,  how- 
ever, be  a  mistake  to  infer  from  this  that  the  nerve  of 
sight  is  really  different  from  the  nerve  of  hearing.  If 
the  matter  is  examined  more  closely,  it  appears  that 
the  nerve  of  sight  cannot  be  excited  by  light.  The 
strongest  sunlight  may  be  allowed  to  fall  on  the  nerve 
of  sight  without  producing  excitement.  It  is  not  the 
nerve,  but  a  peculiar  terminal  apparatus  in  the  retina 
of  the  eye  with  which  the  nerve  of  sight  is  connected, 
which  is  sensitive  to  light.  The  case  of  the  other 
sense-nerves  is  similar ;  each  is  provided  at  its  peri- 
pheric end  with  a  peculiar  receptive  apparatus,  which 
can  be  excited  by  definite  influences,  and  which  then 
transmits  these  influences  to  the  nerves.  On  the 
difference  in  the  structure  of  these  terminal  apparatus 
depend  which  influences  have  the  power  of  exciting 
them.  When  the  excitement  has  once  entered  the 
nerve  it  is  always  the  same.  That  it  afterward  elicits 
different  sensations  in  us,  depends  again  on  the  character 
of  the  nerve-cells  in  which  the  nerve-fibres  end.  Sup- 
posing that  the  nerves  of  hearing  and  of  sight  of  a 
man  were  cut,  and  the  peripheric  end  of  the  former 
were  perfectly  united  with  the  central  end  of  the 
latter,  and  contrariwise  that  the  peripheric  end  of  the 
nerve  of  sight  were  perfectly  imited  with  the  central 


284  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

end  of  the  nerve  of  hearing,  then  the  sound  of  an 
orchestra  would  elicit  in  us  the  sensation  of  light  and 
colour,  and  the  sight  of  a  highly  coloured  picture 
would  eHcit  in  us  impressions  of  sound.  The  sensa- 
tions which  we  receive  from  outward  impressions  are 
therefore  not  dependent  on  the  nature  of  these  im- 
pressions, but  on  the  nature  of  our  nerve-cells.  We 
feel  not  that  which  acts  on  our  bodies,  but  only  that 
which  goes  on  in  our  brain. 

Under  these  circumstances  it  may  appear  strange 
that  our  sensations  and  the  outward  processes  by 
which  they  are  evoked  are  so  entirely  in  agreement ; 
that  light  elicits  sensations  of  light,  sound  sensations 
of  sound,  and  so  on.  But  this  agreement  does  not  really 
exist ;  its  apparent  existence  is  only  due  to  the  use  of 
the  same  name  to  express  two  processes  which  have 
nothing  in  common.  The  process  of  the  sensation  of 
light  bears  no  likeness  to  the  physical  process  of  the 
ether  vibrations  which  elicit  it;  and  this  is  evident 
even  in  the  fact  that  the  same  vibrations  of  ether 
meeting  the  skin  elicit  an  entirely  different  sensation, 
namely,  that  of  warmth.  The  vibrations  of  a  tuning-fork 
are  capable  of  exciting  the  nerves  of  the  human  skin, 
and  then  they  are  felt ;  they  may  excite  our  auditory 
nerves,  and  then  they  are  heard;  and  under  certain 
circumstances  they  may  be  seen.  The  vibrations  of 
the  tuning-fork  are  always  the  same,  and  they  have 
nothing  in  common  with  the  sensations  which  they 
elicit.  Though  the  physical  processes  of  the  vibrations 
of  ether  are  called,  sometimes  light,  and  at  another  time 
heat,  a  more  accurate  study  of  physics  shows  that  the 
process  is  the  same.  The  usual  classification  of  physical 
processes  into  those  of  sound,  light,  warmth,  and  so  on. 


SPECIFIC   ENERGIES   OF   ^•ER\■E-CELLS.  285 

is  irrational,  because  in  these  processes  it  gives  pro- 
minence to  an  accidental  circumstance,  that  is,  to  the 
way  in  which  they  affect  human  beings,  who  are  endowed 
with  various  sensations,  while  in  other,  such  as  mag- 
netic and  electric  processes,  it  is  based  on  quite  different 
marks  of  classification.  Scientific  study  of  the  phy- 
sical processes  on  the  one  hand,  and  of  the  physio- 
logical processes  of  sensation  on  the  other,  exposes  this 
error,  which  penetrates  further  owing  to  the  fact  that 
language  uses  the  same  words  for  the  different  pro- 
cesses, thus  making  their  distinction  harder. 

Language  is,  however,  but  the  expression  of  the 
human  conception  of  things,  and  the  conception  of 
the  innate  identity  of  light  and  the  sensations  of  light, 
of  sound  and  of  the  sensation  of  sound,  and  so  on,  was 
regarded  till  quite  recently  as  incontrovertibly  true. 
Goethe  '  gave  expression  to  this  in  the  lines — - 

Wiir'  nicht  das  Auge  sonnenhaft, 
Die  Sonne  konnt'  es  nie  erblicken ; 
Lag'  nicht  in  uns  des  Gottes  eigne  Kraft, 
Wie  konnt'  uns  Gottliches  entziicken  ! 

Plato  expresses  himself  in  the  same  way  in  the 
'  Timseus.'  On  the  other  hand,  Aristotle  held  correct 
conceptions  on  the  subject.  But  it  is  only  since  the 
researches  of  Johannes  Miiller  laid  new  ways  open  to 
science  that  these  conceptions  have  gained  a  scientific 
foundation,  and  have  been  brought  in  all  points  into 
harmony  with  the  facts,  so  that  they  have  now  become 
the  basis  of  the  physiology  of  the  senses  and  the 
psychology  of  the  present  day. 

One  expression  of  the  erroneous  views  once  pre- 
valent is  to  be  foimd  in  the  theory  of  so-called  ade- 
'  Zahme  Xeiiien,  iii.  70. 


286  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

quale  irritants,  according  to  which  there  is  such  a 
sufficient  irritant  for  each  sense-nerve,  that  is,  an 
irritant  in  its  nature  adapted  to  the  nature  of  the 
sense-nerve,  and  that  this  was  alone  able  to  excite  it. 
We  know  now  that  this  is  not  true.  Yet  the  expres- 
sion may  be  used  to  indicate  the  irritants  which  are 
especially  able  to  act  on  the  terminal  organs  of  the 
nerves. 

In  the  same  way  we  may  look  upon  the  idea  of 
so-called  specific  energies  of  the  sense-nerves,  if  by 
this  it  is  intended  to  express  any  character  of  "  the 
nerves,  as  disproved.  But  we  must  ascribe  specific 
energies  to  the  individual  nerve-cells  in  which  the  sen- 
sations are  originated.  It  is  these  alone  which  are 
able  to  produce  in  us  different  kinds  of  sensation.  If 
all  the  nerve-cells  of  the  sensations  were  alike,  sensa- 
tions could  indeed  be  elicited  in  us  by  the  influence 
of  the  outer  world  on  our  sense  organs ;  but  these 
would  only  be  of  one  and  the  same  kind,  or  at  most  it 
could  only  be  in  the  strength  of  this  one  undefined 
sensation  that  differences  would  be  perceptible.  There 
may  be  animals  which  are  only  capable  of  such  a  single 
undefined  sensation,  their  nerve-cells  being  all  alike 
and  not  yet  differentiated.  Such  animals  would  be 
able  to  form  a  conception  of  the  outer  world  as 
distinguished  from  their  own  bodies,  that  is,  they 
would  be  able  to  evolve  self-consciousness  ;  but  they 
would  not  be  able  to  attain  a  knowledge  of  the  pro- 
cesses in  the  outer  world.  The  development  of  such 
knowledge  in  us  is  greatly  assisted  by  a  comparison 
of  the  different  impressions  brought  about  by  the 
different  organs  of  the  senses.  A  body  presents  itself 
to  our  eye  as  occupying  a  certain   space,  being  of  a 


coxcLusiox.  287 

certain  colour,  and  so  on.  By  tasting  we  may  gain 
further  conceptions  of  this  body.  If  it  is  out  of  reach 
of  our  hands,  by  approaching  it  we  may  observe  how 
the  apparent  size  of  the  body,  as  the  eye  shows  it 
to  us,  increases  as  we  approach.  These  and  many 
thousand  other  experiences  which  we  have  gained 
since  our  earliest  youth  have  gradually  put  us  in  a 
position  to  form  conceptions  as  to  the  nature  of  a  body 
merely  from  a  few  sensations.  In  this  act  many  com- 
plete inferences  are  unconsciously  involved,  so  that 
that  which  we  believe  to  have  been  directly  perceived 
is  really  known  by  inference  from  many  sensations 
and  from  a  combination  of  former  experiences.  For 
instance,  we  think  that  we  see  a  man  at  a  certain  dis- 
tance ;  really,  however,  we  only  feel  a  picture  of  a 
certain  size  of  the  man  on  our  retina.  We  know  the 
average  size  of  a  man,  and  we  know  that  the  apparent 
size  decreases  with  the  distance ;  moreover,  we  feel 
the  degree  of  contraction  of  the  muscles  of  our  eye 
which  is  necessary  to  direct  the  axis  of  our  eye  to  the 
object  and  for  the  adjustment  of  our  eye  to  the  neces- 
sary distance.  From  all  these  circumstances,  the 
opinion,  which  we  erroneously  regard  as  a  direct  sensa- 
tion, is  formed. 

10.  We  have  already  (chap.  iv.  §  2 ;  chap.  vii. 
§  3)  made  acquaintance  with  the  methods  by  which 
Helmholtz  measured  the  details  of  the  time  occupied 
by  the  contraction  of  the  muscle  and  the  propagation 
of  the  excitement  in  the  motor  nerves.  By  the  same, 
or  very  similar  methods,  Helmholtz,  and  others  after 
him,  determined  the  propagation  of  the  excitement  in 
sensory  nerves,  and  found  that  it  was  about  30  m.  per 
second,  and  therefore,  at  nearly  the  same  rate  as  in  the 


288  PHYSIOLOGY    OF   MUSCLES   A^B   NERVES. 

motor  nerves  of  men.  More  than  this  has  been  done: 
the  time  has  been  measured  which  is  requisite  for  an 
irritant  conducted  to  the  brain  to  be  transmuted  into 
consciousness.  Such  determinations,  in  addition  to 
their  theoretical  value,  are  of  practical  interest  to 
observing  astronomers.  In  observing  the  passage  of 
stars  on  the  meridian  and  comparing  the  passage  seen 
through  the  telescope  with  the  audible  beats  of  a 
second-pendulum,  the  observer  always  admits  a  slight 
error,  dependent  on  the  time  which  the  impressions  on 
the  two  senses  require  to  reach  the  state  of  conscious- 
ness. In  two  different  observers  this  error  is  not  of 
exactly  the  same  value  ;  and  in  order  to  render  the 
observations  of  different  astronomers  comparable  with 
each  other,  it  is  necessary  to  know  the  difference 
between  the  two  cases,  the  so-called  personal  equation. 
In  order  to  refer  the  observations  made  by  each  indi- 
vidual to  the  correct  time,  it  is  necessary  to  determine 
the  error  which  is  made  by  each  individual. 

Let  us  suppose  that  an  observer  sitting  in  complete 
darkness  suddenly  sees  a  spark,  and  thereupon  gives 
a  signal.  By  a  suitable  apparatus,  both  the  time  at 
which  the  spark  really  appeared  and  that  at  which  the 
signal  was  given  are  recorded.  The  difference  between 
the  two  can  be  measured,  and  it  is  called  the  physio- 
logical time  for  the  sense  of  sight ;  the  physiological 
time  for  the  sense  of  hearing  and  for  that  of  touch 
may  be  determined  in  the  same  way.  Thus  Professor 
Hirsch,  of  Neufchatel,  found — 

In  the  case  of  the  sense  of  sight     0*1974  to    0-2083  sec. 
„  „        hearing  0*194  „ 

„  „        touch     0"1733  „ 

"WTien  the  impression  which  was  to  be  recorded  was 


CONCLUsio:^.  289 

not  unexpected,  but  was  known  beforehand,  the  physio- 
logical time  proved  to  be  much  shorter ;  in  the  case 
of  the  sense  of  sight  it  was  only  from  0*07  to  O'll  of 
a  second.  From  this  it  follows  that,  in  the  case  of 
excitement  the  advent  of  which  is  expected,  the  brain 
fulfils  its  work  much  more  quickly. 

Certain  experiments  made  by  Donders  are  yet  more 
interesting.  A  person  was  instructed  to  make  a  signal, 
sometimes  with  the  right  hand,  sometimes  with  the 
left,  according  as  a  gentle  irritant  applied  to  the  skin 
was  felt  in  one  place  or  the  other.  If  the  place  was 
known,  the  signal  succeeded  the  irritant  after  an  in- 
terval of  0"205  of  a  second,  but  if  the  place  was  not 
known,  only  after  an  interval  of  0*272  of  a  second.  The 
psychological  act  of  reflection,  as  to  where  the  irritant 
occurred,  and  that  of  the  corresponding  choice  of  the 
hand  occupied,  therefore,  a  period  of  0*067  of  a  second. 
The  physiological  time  in  the  case  of  the  sense  of 
sight  was  somewhat  dependent  on  colour ;  white  light 
was  always  noticed  somewhat  sooner  than  red.  If  the 
observer  knew  the  colour  which  he  was  to  see,  he  gave 
the  siofnal  sooner  than  when  this  was  not  the  case  and 
he  had  first  to  reflect  as  to  what  he  had  seen  before  he 
gave  the  signal.  In  such  experiments,  the  observer 
always  forms  a  preconception  of  the  coloiur  which  he 
,  expects  to  see.  If  the  colour  when  it  becomes  obser- 
vable coiTesponds  with  that  which  he  expected,  the 
reaction  in  the  observer  takes  place  sooner  than  when 
this  is  not  the  case. 

Similar  observations  were  made  in  the  case  of  the 
sense  of  hearing :  the  recognition  of  any  sound  heard 
follows  sooner  when  it  is  known  beforehand  what  sound 
is  to  be  heard  than  when  this  is  not  the  case. 


290  PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 

This  sluggishness  of  the  consciousness,  if  we  may  so 
call  it,  is  exhibited  in  another  way  in  certain  experi- 
ments instituted  by  Helmholtz.  The  eye  sees  a  figure, 
which  is  immediately  followed  by  a  bright  light :  the 
more  powerful  the  latter  is,  the  longer  must  the  iirst 
have  been  seen,  if  it  is  to  be  recognised  at  all ;  more- 
over, complex  figures  require  more  time  than  simpler. 
If  letters  are  seen  lighted  up  on  a  bright  ground  for  a 
very  short  time,  no  other  light  following,  a  shorter  time 
is  necessary  for  the  recognition,  the  larger  are  the  letters 
and  the  brighter  the  illumination. 

It  is  true  that  it  is  only  very  simple  brain  activities 
the  origin  of  which  can  be  in  any  way  made  clearer  by 
such  experiments  as  these ;  but  yet  these  are  the  rudi- 
ments of  all  mental  activity — sensation,  conception,  re- 
flection, and  will;  and  even  the  most  elaborate  deduction 
of  a  speculative  philosopher  can  only  be  a  chain  of  such 
simple  processes  as  those  which  we  have  been  observ- 
ing. These  measurements,  therefore,  represent  the 
beginnings  of  an  experimental  physiological  psychology, 
the  development  of  which  is  to  be  expected  in  the 
future.  It  seems  to  me  that  remunerative  study  of 
the  processes  in  nerve-cells  must  start  from  the  very 
simplest  phenomena.  Eesults  are,  therefore,  to  be  first 
looked  for  in  the  study  of  the  .processes  of  reflection ; 
possibly  these  will  prepare  the  ground  on  which  at  some 
future  time  a  mechanism  of  the  nervous  processes  may 
be  built.  '  In  truth,'  says  D.  F.  Strauss,  in  '  The  Old 
and  the  New  Faith,'  '  he  who  shall  explain  the  grasp 
of  the  polyp  after  the  prey  which  it  has  perceived,  or 
the  contraction  of  the  insect  larva  when  pierced,  will 
indeed  be  yet  far  from  having  in  this  comprehended 
human  thought,  but  he  will  be  on  the  way  to  do  so,  and 


CONCLUSION.  291 

may  attain  his  end  without  requiring  the  help  of  a 
single  new  principle.'  Whether  this  end  will  ever  be 
attained  is  another  matter.  But  we  can  always  gain 
fuller  knowledge  of  the  conditions  under  which  it  may 
come  to  pass,  and  of  the  mechanical  processes  which 
form  its  first  principles.  Such  is  the  lofty  aim  after 
which  the  science  of  the  General  Physiology  of  Muscles 
and  Nerves  strives — an  aim  worthy  of  the  labour  of  the 
noblest. 


NOTES    AND    ADDITIONS 


1.  Graphical   Represextatiox.      Idea  of  Mathematical 
Function  (p.  49), 

The  method  employed  in  fig.  16  of  representing  by  a 
sign  the  dimensions  of  the  expansion  relatively  to  the  amount 
of  the  expanding  -weights,  admits  of  such  a  vai-iety  of  appli- 
cations, and  will  be  used  so  frequently,  that  a  brief  explana- 
tion of  it  may  not  be  out  of  place  here. 

"When  two  series  of  values  bear  such  a  relation  the  one 
to  the  other  that  each  value  of  one  series  corresponds  with  a 
definite  value  in  the  other,  mathematicians  speak  of  the  one 
value  as  the  function  of  the  other.  This  relation  may 
always  be  exhibited  in  tabular  form,  as  in  the  following 
example : — 

1234       5       6       7       8       9     10 
2     4     6     8     10     12     14     16     18     20 

The  relation  which  prevails  in  this  case  is  very  simple. 
Each  number  in  the  uj^per  series  corresponds  with  a  number 
in  the  lower,  and  the  latter  is  always  double  the  value  of 
the  former.  Representing  the  numbers  in  the  upper  series 
by  X,  those  in  the  lower  by  y,  the  relation  between  the  two 
series  of  numbers  may  be  expressed  in  the  formula  : 

y=2x 
This  formula  expresses  the  same  and  even  more  than  the 


294  PHYSIOLOGY    OF    MUSCLES   AND    NERVES. 

table.  Substituting  for  tbe  unknown  x,  wMch  may  repre- 
sent any  number,  the  number  4,  then  the  table  expresses 
that  the  value  of  the  corresponding  y  is  8.  If  x=5,  then  the 
table  expresses  that  3/= 10.  But  when  the  value  of  x  is 
intermediate  between  4  and  5,  e.g.  4-2371,  the  table  does  not 
help  us;  but  by  the  use  of  the  formula  the  value  of  the 
corresponding  y  may  easily  be  found ;  it  is  =  8'4742. 
The  formula  may  be  reversed,  and  written  thus  : 

that  is  to  say,  for  any  given  value  of  y  we  may  calculate  the 
corresponding  value  of  x.  It  is  exactly  the  same  in  the  case 
of  the  similar  formula  : 

y^-3x,  ■ 

which  may  also  be  written  thus  : 
x=^y. 

In  this  case,  therefore,  with  each  given  value  of  x  corresponds 
a  certain  value  of  y,  the  latter  beiug  three  times  the  value 
of  the  former.     In  the  two  corresponding  formulae 

,         1 

y  =  ax  and  a;=— y, 
a 

is  a  somewhat  wider  expression  to  this  kind  of  relation ;  in 
this  case  x  and  y  are  again  the  signs  of  the  two  correspond- 
ing series  of  numbers,  a  expresses  a  definite  figure  which  is  to 
be  i-egarded  as  unchangeable  within  each  particular  case.  In 
our  first  example  a=2,  in  our  second  example  a=:3,  and 
similarly  in  any  other  instance  a  may  have  any  other  value. 
Lookinjf  now  at  the  followins:  table  : 


1 

2     3 

4 

5 

6  etc. 

1 

4     9 

16 

25 

36  etc. 

we  see  that  any  number  in  the  lower  series  is  found  by 
multiplying  the  corresponding  number  in  the  upper  series  by 
itself,  as  may  be  expressed  iu  the  formula 

y^x  X  or  y=X' 


NOTES    AND    ADDITIONS. 


295 


This  formula  when  reversed  appears  thus  : 

Provided  with  a  formula  of  this  sort,  which  expresses  the 
mutual  relation  of  two  corresponding  seiies  of  values,  it  is 
always  possible  to  draw  out  a  table,  though,  on  the  contrary, 
the  relation  laid  down  in  the  table  cannot  always  be  ex- 
pressed in  a  formula,  for  the  relations  are  not  always  as 
simple  as  in  our  examples.  Generally  the  values  which  are 
treated  in  the  table  are  such  as  have  been  found  by  observa- 
tions, as  for  instance  in  our  case,  the  expansion  of  the  muscle 
caused  by  various  weights.  With  each  weight  an  expansion 
corresponds,  and  this  is  found  by  experiment  and  may  be 
expressed  in  tabular  form,  thus  : 

Weight :       50       100     1.50  200      250  300  grm. 
Expansion  :     3-2        6         8       9-5      10     10-5  mmt. 

A      A'       A"        A'"  r 


b 


\ 

c 

c 

r" 

c" 

\ 

I" 

ol" 

fl'" 

d 

\^^ 

^\^ 

b 

iT^ 

"~~-j^^ 

~^~~.^_^^ 

// 

''  ^ — ^- 

^^---^ 



Fig.  69.     GRArmcvL  repkesentatiox  of  muscle-expansiox. 


All  that  is  shown  by  the  table  is  that  the  expansion  does 
not  increase  proportionately  with  the  Aveight  (as  would  be 
the  case  in  inorganic  bodies),  but  increase  in  a  continually 
decreasing  proportion.  But  any  required  function-character, 
whether  it  is  expressed  by  a  comparison  or  in  a  table  drawn 
up  on  the  basis  of  observations,  may  be  diagrammatically 


296  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

shown  by  a  inetliod  first  employed  by  Descartes,  whicli  it  is 
our  present  object  to  explain. 

The  amounts  treated  may  be  of  tbe  most  varied  kinds  : 
numbers,  weights,  degrees  of  warmth,  tbe  number  of  births 
or  deaths,  and  so  on.  In  all  cases  the  amount  may  be  diagram- 
matically  shown  by  the  length  of  a  line.  If  a  line  of  a  cer- 
tain length  represents  any  given  amount,  then  double  this 
amount  is  represented  by  a  line  twice  the  length  of  the 
former.  It  does  not  matter  what  is  the  standard  selected ; 
but  when  once  selected  it  must  not  be  varied  in  the  same 
representation.  Two  Hnes  are  drawn  at  right  angles  to 
each  other ;  from  the  point  of  section  B  (fig.  69)  the  lengths 
which  are  to  represent  the  values  of  one  series  (in  our  case, 
the  weights  attached  to  the  muscle)  are  measured  off  on  the 
e 
^  f 


A 

Fig.  70.  Diagrah  of  positive  axd  negative  values. 
horizontal  Hne.  From  each  of  the  points  thus  obtained,  d',  h", 
d",  d'",  a  line  is  drawn  at  right  angles  to  the  first,  care  being 
taken  to  make  its  length  express  the  expansion  corresponding 
with  each  weight  respsctively.  This  gives  the  lines  d'  B', 
h"  B",  d"  B'",  d'"  B^",  By  connecting  these  points  we 
obtain  the  cirrve  BB'  B"  B'"  B'"'  x",  which  at  a  glance 
shows  the  relation  between  the  weight  and  the  expansion. 
In  exactly  the  same  way  the  curve  h  V  h"  h'"  B''  y  is  pro- 
jected, and  this  represents  the  expansion  of  the  active  muscle 
by  the  corresponding  weights. 

In  many  cases  it  is  required  to  represent  values  of  oppo- 
site kinds.  If,  for  example  (fig.  70),  the  wire  a  6  is  tra- 
versed by  an  electric  current,  then  one  half  assumes  positive 
tension,  the   other  negative  tension.     To  express  this,  the 


NOTES  A2s'D   ADDITIONS. 


297 


lines  which,  are  to  represent  positive  tension  are  drawn 
upward,  those  which  are  to  represent  negative  tension  down- 
■ward,  from  the  basal  line.  The  figure  then  shows  that 
the  tension  in  the  middle  of  the  wire  =  0,  and  that  toward 
the  left  the  positive,  toward  the  right  the  negative,  tensions 
increase  regularly.  In  order  to  find  the  amount  of  the 
tension,  prevailing  at  any  particular  point,  e.g.  at  e,  a  per- 
pendicular line  is  erected  at  that  point;  and  the  length 
of  this,  e  f,  accurately  represents  the  tension  there  pre- 
vailing. 


2.  Direction  of  the  Muscle-Fibres,  Height  of  Elevatiox, 
AND  the  Accomplishment  of  Work  (p.  93). 

Because  of  the  extreme  rarity  of  long  parallel-fibred 
muscles,  it  is  interesting  to  examine  more  closely  the  in- 
fluence wliich  oblique  arrangement  of  the  „ 
fibres  exercises  on  their  force,  height  of  ele- 
vation, and  on  the  work  which  they  accom- 
plish. AVhen  a  muscle-fibre  is  so  arranged 
that  it  is  incapable  of  efiecting  a  movement 
in  the  direction  of  its  own  contraction,  only  a 
part  of  the  force  of  tension  which  is  generated 
in  it  by  its  contraction  comes  into  play,  and 
this  part  may  be  easily  found  by  the  law  of 
the  parallelogi-am  of  forces.  This  is  the  case 
in  all  simply  and  doubly  psnniform  muscles. 
Supposing  that  the  muscle-fibre  A  B  (fig.  71) 
contracts  to  the  extent  B  h,  but  that  motion 
of  the  point  B,  on  account  of  the  attachment 
of  the  muscle  to  the  bone,  and  of  the  nature 
of  the  sockets  of  the  latter,  can  only  occur  in  -^  _ 
the  direction  B  C ;  in  that  case  the  muscle-  okobi.iquemus- 
fibre,  in  contracting,  undergoes  a  change  in  ci-e-fibkes. 
direction  from  its  fixed  point  of  origin  A,  and  thus  assumes 
the  position  A  h' ;  the  elevation  which  is  really  effected  is, 
14 


298  PHYSIOLOGY    OF   MUSCLES   AND    NERVES. 

therefore,  B  V.     The  small  triangle  BhV  may  be  regarded 
as  a  right-angled  triangle.     This  gives 

sm  p 

The  force  with  which  the  muscle-fibre  strives  to  contract 
in  the  direction  A  B  being  called  h,  only  part  of  this  force, 
the  component  k'  lying  in  the  direction  B  C,  finds  expression. 
According  to  the  law  of  the  parallelogram  of  forces,  this  com- 
ponent is 

k'=  k  sin  j). 

This  force  may  be  regarded  as  proportionate  to  the 
weight  which  the  muscle-fibre  is  able  to  raise  to  the  given 
height  of  elevation.  If  we  then  calculate  the  woi'k  which 
the  muscle  can  accomplish,  we  find,  if  the  motion  can  take 
place  in  the  direction  A  B, 

A=Bbk; 

but  if  motion  can  only  occur  in  the  direction  B  C, 

A  =  Bh'  k'  =  -^^  k  si7ii3=Bb  k. 
sm  J3 

The  value  in  the  two  cases  is  therefore  exactly  the  same, 
or,  in  other  words,  the  amount  of  work  accomplished  by  the 
muscle  is  quite  independent  of  the  direction  in  which  its 
action  takes  place.  This  is,  naturally,  true  of  every  other 
muscle-fibre,  and,  consequently,  of  the  whole  muscle.  The 
statements  which  we  have  made  of  parallel-fibred  muscles 
are  therefore  also  true  of  those  of  which  the  fibres  are  irre- 
gular. The  possible  height  of  elevation  is  always  greater 
the  longer  the  fibres  are,  and  the  force  proportionate  to  the 
diameter  or  to  the  number  of  the  fibres.  In  oblique-fibred 
muscles  the  fibres  are  generally  very  short,  but  very  nume- 
rous ;  these  must,  therefore,  whatever  their  accidental  form, 
be  regarded  as  short  and  thick  muscles,  possessed  of  small 
elevation  and  great  force. 


NOTES   AND    ADDITIONS.  299 


3.  Excitability  and  Strength  of  Ireitant.    CoMBixATioy 
OF  Irritants  (p.  119). 

When  the  coils  of  a  sliding  inductive  apparatus  ai'o 
brought  nearer  together,  the  strength  of  the  inductive  current 
does  not  increase  in  exact  proportion  with  the  decreasing 
distance  betweeen  the  two,  but  in  a  complex  way,  -which 
must  b3  provided  for  in  each  apparatus  separately.  Pick, 
Kronecker,  and  others  have  shown  methods  by  which  this 
calibration  of  the  apparatus  may  be  accomplished.  If  the 
real  strength  of  the  irritating  current  is  compared  with 
the  height  of  the  pulsation  which  it  elicits,  it  appears  that 
when  the  current  is  very  weak  no  action  is  observable; 
action  first  appears,  in  the  form  of  a  slight,  just  a- isible  pulsa- 
tion, when  the  current  has  reached  a  certain  strength,  greater 
or  less  according  to  the  condition  of  excitability  of  the 
nei've.  As  the  cui-rents  increase  further  in  strength,  the 
lieights  of  elevation  increase  in  exact  proportion  to  the 
strength  of  the  currents,  till  a  certain  maximum  has  been 
reached.  If  the  strength  of  the  current  becomes  yet  greater, 
the  pulsations  remain  constant  for  a  time;  but  then  they 
again  increase  and  reach  a  second  maximum,  above  which 
they  do  not  pass. 

These  so-called  '  over  maximum  '  pulsations  are  due  to 
a  combination  of  two  ii*ritants.  An  inductive  shock  is,  as 
we  have  seen,  a  very  brief  current,  in  which  the  commence- 
ment and  the  end  succeed  each  other  very  rapidly.  For 
reasons  which  will  be  further  explained  in  ISTote  7,  the  com- 
mencement of  an  inductive  ciu-rent  is  a  more  powerful 
irritant  than  its  end.  As  long,  therefore,  as  the  current 
does  not  pass  a  certain  strength,  only  the  commencement  of 
the  current  irritates ;  but  in  the  case  of  very  powerful  cur- 
rents the  end  may  be  suflficiently  effective :  this  gives  two 
initations  following  each  other  in  rapid  succession,  and  these 


300  PHYSIOLOGY    OF    MUSCLES   AND   NERVES. 

together  effect  a  greater  pulsation  than  does  a  single  irrita- 
tion. 

If  more  than  two  irritants  follow  each  other  in  rapid 
succession,  tetanus  results,  as  we  know.  In  this  case  also 
the  height  of  elevation  is  always  greater  than  that  which 
can  be  attained  by  a  single  pulsation.  For  the  muscle  has 
the  power  of  being  again  ii-ritated  even  when  it  is  ah-eady  in 
the  act  of  contraction,  a  more  powerful  contraction  being 
thus  induced  in  it.  The  bearing  of  these  facts  on  the  case 
of  nerve  is  that  the  separate  excitements  effected  in  it  by 
these  rapidly  successive  irritations  do  not  mutually  disturb 
each  other,  but  are  transmitted  one  after  the  other,  in  the 
sequence  in  which  they  originate,  to  the  muscle  on  which 
they  act.  But  when  the  number  of  the  irritants  becomes 
too  great,  the  nerve-molecules  are  no  longer  able  to  keep 
pace  with  the  rapidly  succeeding  shocks,  and  the  nerve  is 
vmexcited.  The  limit  at  which  this  intervenes  has,  how- 
ever, not  yet  been  determined  with  any  certainty.  It 
appears  to  lie  at  between  SOO  to  1000  irritants  per  second. 

4.  Curve  of  Excitability.    Eesistance  to  Transmissiost 
(p.  123). 

The  increased  excitability  at  the  upper  parts  of  the  un- 
injured sciatic  nerve,  when  not  severed  from  the  body, 
which,  on  the  strength  of  our  earlier  experiments,  we  have 
assumed  in  the  text,  has  recently  been  again  defended  by 
Tiegel  against  various  objections.  For  reasons  explained  in 
the  text  it  is  inadmissible  to  infer  an  avalanche-like  increase 
in  the  irritation  merely  from  this  higher  excitability  of  the 
upper  parts.  Beside  the  experiments  of  Munk  alluded  to 
on  page  116,  there  are  other  experimeqts  from  which  a 
resistance  to  transmission  in  the  nerve  may  be  inferi'ed. 
Such  a  resistance,  weakening  the  iiTitant  during  its  propa- 
gation, and  an  avalanche-like  increase  in  the  irritant,  are 
irreconcilable  contradictions  which    mutually  exclude  each 


NOTES   AND    ADDITIONS.  301 

otlier.  If  resistance  to  transmission  can  be  shown,  then  the 
irritation  cannot  increase  in  strength  during  its  propagation 
through  the  nerve.  I  will,  therefore,  here  briefly  mention 
the  reasons  which  induce  me  to  declare  in  favour  of  one,  and 
against  the  other,  of  these  assumptions. 

As  is  mentioned  on  p.  141,  transmission  becomes  con- 
sidei'ably  harder  when  the  nerve  is  in  an  anelectrotonic 
condition,  and  in  strong  anelectrotonus  it  is  even  rendered 
altogether  impossible.  It  is  natural  to  regard  this  greatrr 
difiiculty  as  an  increase  of  a  resistance  already  present,  A 
more  impoi-tant  reason  is  however  to  be  found  in  the  phe- 
nomena which  occur  in  reflex  actions.  If  a  sensory  nerve 
is  irritated,  the  excitement  can  be  ti-ansmitted  to  the  dorsal 
marrow  and  the  brain,  where  it  may  be  transferred  to  a 
motor  nerve  (cf.  p.  274).  This  transference  always  occupies 
a  considerable  time,  which  I  call  reflex-time.  If  a  sensoiy 
nerve  is  initated  sufficiently  to  cause  a  poweif ul  reflex  action 
(called  a  'suflicient  ii-ritant '),  if  the  reflex-time  in  this  case  is 
determined,  and  if  irritants  of  continually  increasing  strength 
are  then  allowed  to  act  on  the  same  point  in  the  nerve, 
then  the  reflex-time  is  found  to  become  continually  shorter. 
If,  however,  a  point  in  the  nerve  lying  very  near  the  dorsal 
marrow  is  irritated,  then  even  in  the  case  of  a  '  sufiicient 
irritant '  the  reflex-time  is  short.  It  is  evident  that  the 
duration  of  the  reflex-time  depends  on  the  strength  of  the 
iri'itant  when  it  reaches  the  dorsal  marrow.  The  irritant 
which  comes  from  the  point  in  the  nerve  adjacent  to  the 
dorsal  marrow  is  but  slightly  affected ;  but  that  coming 
from  a  more  remote  point  is  weakened ;  so  that  a  much 
stronger  irritant  must  be  applied  to  these  more  remote  point«!, 
if  an  equally  short  reflex-time  is  to  be  attained. 

It  is  true  that  these  observations  have  been  made  with 
sensory  nerves.  But  owing  to  the  entirely  similar  character 
exhibited  by  all  kinds  of  nerve-flbres  in  all  points,  where 
comparison  is  possible,  we  are  justified  in  applying  the  views 
thus  gained  to  the  motor-nerves.     It  is,  at  all  events,  im- 


302 


PHYSIOLOGY    OF   MUSCLES    AND    NERVES. 


probable  that  in  one  nerve-fibre  a  resistance  to  transmission 
exists,  and  in  another  an  avalanche-like  increase.  All  the 
facts  are  more  easily  and  simply  explained  by  assuming  that 
there  is  a  resistance  to  transmission  in  all  nerves,  allowance 
being  at  the  same  time  made  for  the  difference  in  the  ex- 
citability of  different  points  in  the  nerve. 

Moreover  the  curve  of  excitability  in  the  case  of  the 
sciatic  nerve  is  not  a  simple  ascending  line  from  the  muscle 
to  the  dorsal  marrow.  This  nerve  is  found,  as  is  shown  in 
fig.  72,  by  the  union  of  several  roots;  it  then,  at  various 


Fig.  72.    The  sciatic  xerve  and  calf-muscle  of  a  frog. 

points,  gives  off  branches  which  enter  the  muscles  of  the 
upper  leg,  and  then  separate  into  two  branches,  one  of  which 
provides  for  the  calf-muscle  {gastrocnemius),  the  other  for  the 
flexor  muscle  of  the  lower  leg.  If  various  points  of  this 
nerve  are  irritated  in  the  living  animal,  the  nerve  having 
been  merely  exposed  and  isolated  from  the  surrounding  parts, 
but  not  separated  from  the  dorsal  marrow,  it  is  very  evident 
that  the  excitability  at  the  upper  jDoints  is  generally  greater 
than  at  the  lower  ;  but  points  are  also  fou.nd  in  the  course 
of  the  nerve  at  which  a  gi^eater  excitability  exists  than  at  the 
points  above  and  below,  as  also,  on  the  contrary,  a  less  ex- 
citability than  at  the  adjacent  points.  Such  irregularities 
are  most  abundantly  exhibited  at  the  points  where  nerve- 
branches  separate  from  the  main  trunk,  especially  when  these 
branches  have  been  cut  away.  This  is  partly  due  to  elec- 
trotonic  influences  {cf.  p.  125  et  seq.  ;  p.  21-5  et  seq.,  Note  13). 
The  nerve- fibres  which  are  cut  generate  a  current  which 


NOTES   AND    ADDITIONS.  303 

passes  through  those  which  are  not  cut  off,  those  the  excita- 
bility of  which  is  tested,  and  alters  their  excitability.  This 
influence  changes  in  the  whole  mass,  as  the  cut  nerves  die, 
thus  giving  rise  to  irregularitiss  the  further  nature  of  which 
we  need  not  trace. 


5.  Ikfluence   of   the   Length   of   the   Portio::  of  the 
Nerve  excited  (p.  138). 

If  the  irritant  reroains  the  same,  the  longer  is  the  portion 
of  the  nerve  irritated,  the  stronger  is  the  action  on  the 
muscle.  If  the  excitability  of  a  portion  of  the  nerve  is  found 
by  the  method  of  minimum  iriitants,  that  is,  if  the  weakest 
irritant  capable  of  effecting  an  observable  pulsation  is  looked 
for,  and  if  various  degrees  of  excitability  prevail  in  the  por- 
tions of  the  nerve  simultaneously  exposed  to  the  irritant, 
action  may  result,  even  if  only  a  part  of  the  portion  of  nerve 
is  really  excited ;  in  reality,  therefore,  it  is  but  the  excita- 
bility of  the  most  excitable  part  of  the  whole  nerve-portion 
which  is  tested.  In  a  fresh  nerve  this  is  generally  the  upper 
part  of  the  nerve-portion.  But  when  there  is  no  great  dif- 
ference in  excitability  within  the  nerve-portion,  then  every 
part  of  the  poi'tion  will  be  excited  by  an  irz'itant  of  a  certain 
strength  in  an  approximately  like  manner,  and  the  action 
observed  in  the  muscle  will  therefore  be  the  combined  effect 
of  the  excitement  of  the  separate  parts  of  the  nerve-portion. 
But  if,  as  we  have  assumed,  the  loss  of  excitability  in  each 
part  follows  the  highest  excitability  very  suddenly,  the  effect 
must  be  that  the  portion  actually  in-itated  continually  be- 
comes shorter;  tlie  parts  which  ai'c  irritated  are  however 
still  in  the  highest  state  of  excitability,  and  therefore  exhibit 
the  third  stage  of  pulsatioji  (the  testing  current  having  been 
so  chosen  that,  in  the  fresh  nerve,  it  originally  produced  the 
first  stage).  The  form  in  which  the  third  stage  exhibits  itself 
— pulsation  on  the  closing  of  a  descending  curi-ent  and  on  the 
opening  of  nn   ascending   current —  must   therefore  remain 


304  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

tinclianged,  but  the  pulsations  must  gradually  decrease  in 
strength,  and  all  effect  must  finally  disappear,  just  when 
tlie  maximum  of  excitability,  and  the  death  which  follows 
this,  pass  the  lower  limit  of  the  excited  port'on. 


6.     Difference   between   Closing   and    Opening    Induc- 
tive Currents.     Helmholtz's  Arrangement  (p.  151). 

When  an  electric  current  is  suddenly  closed  in  a  spiral, 
this  not  only  acts  inductively  on  a  neighbouring  spiral,  but 
the  individual  coils  of  the  2)rimary  spii'al  act  inductiA'ely  on 
each  other ;  an  analogous  effect  wonld  occur  on  the  opening, 
but  that  the  sudden  interruption  of  transmission  prevents  the 
development  of  this  opening  inductive  current  in  the  primary 
coil.  The  inductive  current  which  originates  on  the  closing 
of  the  current  being  in  an  opposite  direction  to  the  closed 
I  current  itself,  the  former  must  weaken  the  latter ;  the  cur- 
rent can  therefore  attain  full  strength,  not  at  once,  but  only 
gradually  ;  but  on  the  opening  the  current  suddenly  ceases. 
This  difference  in  the  duration  of  the  closing  and  opening 
of  the  j)rimary  current  corresponds  with  differences  in  the 
currents  induced  by  them  in  the  secondary  spiral,  which  are 
used  for  the  irritation  of  the  nerve.  Figui'e  73  exhibits  these 
characters.  The  upper  part  of  the  figure  represents  the  tem- 
poral course  of  the  main  current  in  the  primary  spiral  of  an 
inductive  apparatus ;  the  lower  part  repres3nts  the  temporal 
course  of  the  induced  currents  in  the  secondary  spiral.  The 
line  0  . .  .0  . .  .t  represents  the  duiation.  The  piimary  current 
is  closed  at  the  moment  o.  Were  the  retardatoiy  influence 
which  has  been  mentioned  not  present  in  the  primary  spiral, 
the  current  would  at  once  attain  its  full  strength  0  J ;  but 
owing  to  that  influence  it  attains  this  strength  only  gradually, 
somewhat  as  shown  by  the  crooked  line  .3.  With  this  gradu- 
ally occurring  cuiTont  corresponds  a  closing  inductive  curi-ent 
in  the  secondary  spiral,  as  is  represented  by  the  curve  4 ; 


NOTES    AXD    ADDITIONS. 


305 


the  curve  is  drawn  dov/uward  from  the  time-line  o  . .  .o  .  .  .  t, 
to  indicate  that  the  direction  of  this  induced  current  is 
opposed  to  the  direction  of  the  primary  current.  If  the 
primary  current  is  interrupted,  it  suddenly  falls   from  the 


■^ 

/  • 

/0| 

>< 

si 

/ 

1      / 

N  1 

^ 

strength  J,  as  inuicated  by  the  straight  line  1.  With  this 
fall  corresponds  an  inductive  current,  which  suddenly  rises 
very  abruptly  and  again  falls  somewhat  less  abruptly,  as 
shown  in  curve  2.  From  this  it  is  evident  that  the  latter 
must  be  physiologically  much  more  elleetive  than  the  former. 


306  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

Occasionally  it  is  desirable  to  remove  this  difference,  and 
to  provide  two  inductive  currents  whicli  flow  and  act  nearly 
in  the  same  way.  This  may  ba  managed,  if,  instead  of 
closing  and  interrupting  the  current  of  the  primary  coil,  an 
additional  closing  wire  offering  small  resistance  is  provided, 
and  the  interruption  is  effected  in  this.  If  this  additional 
apparatus  is  pi-esent,  only  a  very  small  part  of  the  current 
passes  through  the  primary  coil.  The  strength  of  this  part  is 
indicated  by  J,  J,.  When  the  closing  in  the  additional  ap- 
paratus is  interruj)ted,  the  primary  current  slowly  increases 
in  strength  from  </,  to  J  as  shown  by  the  dotted  curve  5 ; 
with  this  increase  corresponds  an  inductive  current  in  the 
secondary  coil,  as  represented  by  curve  6.  If  the  closing  of 
the  additional  apparatus  is  once  more  effected,  the  current  in 
the  primary  coil  sinks  in  strength  from  J  to  J,;  but  the  so- 
called  extra  current,  that  which  originates  in  consequence  of 
the  sinking  in  the  primary  coil,  is  now  able,  the  coil  being 
closed,  to  take  effect,  and,  as  its  direction  is  the  same  as  that 
of  the  main  current,  it  retards  the  sinking  of  the  latter,  so 
that  this  now  takes  place  as  indicated  by  curve  7 ;  and  with 
this  slow  sinking  of  the  main  current  corresponds  an  induc- 
tive current  in  the  secondary  coil,  such  as  is  shown  by 
curve  8. 

Helmholtz  made  an  alteration  in  du  Bois-Reymond's 
sliding  inductive  appai-atus  by  means  of  which  this  ad- 
ditional closing  and  opening  is  automatically  accomplished. 
He  adapted  Wagner's  hammer  for  this  purpose,  as  shown  in 
fig.  74.  The  current  of  the  apparatus  K  passes  through  the 
wire  arranged  between  g  and  f  to  the  primary  coil  c,  from 
this  to  the  coils  round  the  small  electro-magnet  h,  and  from 
the  latter  through  the  column  a,  back  to  its  original  starting 
point.  The  electro-magnet  attracts  the  hammer  h,  in  con- 
sequence of  which  a  small  platinum  plate  fastened  below 
the  German  silver  spring  is  brought  into  contact  with  the 
platinum  point  of  the  screw/,  thus  completing  a  brief  and 
efficient  additional  closm-e  g^f^  a.     The  consequence  of  this 


NOTES    AND    ADDITIONS. 


307 


is  that  the  curreut  in  the  coil  c,  and  at  the  same  time  in  the 
electro-magntit;  is  much  weakened;  the  latter  can  no  longer 
attract  the  hammer,  which  springs  upward,  so  that  the  plate 
is  removed  from  the  point  /  and  the  additional  closure  is 
interrupted .  The  current  once  more  passes  in  full  strength 
through  the  coil  c  and  the  electro-magnet  b,  the  hammer  is 
again  attracted,  and  the  whole  process  is  repeated  as  long  as 
the  circuit  K  endures.     If  it  is  required  to  restore  the  appa- 


FlG.  74.      IIeLMHOLTZ's   ArPAR.VTUS. 


ratus  to  its  oiiginal  condition,  it  is  only  necessary  to  remove 
the  wire  g^,  and  to  lower  the  point/". 


7.    ACTIOX  OF  CUKREXTS  OF  SlIOUT    DuRATIOX    (p.   152). 

Either  the  clo.sing  or  opening  of  a  continuous  current 
or  an  inductive  current  is  used  to  excite  the  nerve.  In  the 
latter  case,  however,  as  has  already  been  indicated  in  Note 


308  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

3,  we  liave  reallj^  to  do  with  a  closing  immediately  suc- 
ceeded by  an  opening,  for  the  inductive  current  arises  and 
again  disappears  as  soon  as  it  has  reached  a  certain  strength. 
This  may  be  imitated  with  suitable  apparatus,  by  closing  a 
constant  current  for  a  very  biief  time.  Such  a  '  current 
shock  '  may  exhibit  exactly  the  same  phenomena  as  does  an 
inductive  current.  If  its  duration  remains  unaltered,  but 
the  strength  of  the  cun-ent  is  gradually  increased,  the  height 
of  elevation  at  iirst  increases,  remains  for  a  time  at  a  first 
maximum,  after  which  it  again  increases  and  reaches  a  second 
maximum.  The  explanation  is  the  same  as  was  given  in 
Note  3  for  inductive  currents.  At  first  only  the  beginning 
of  the  cun-ent  (the  closing)  acts  excitingly;  but  when  the 
current  is  stronger,  the  cessation  of  the  current  (the  opening) 
can  also  act  in  the  same  way,  and  a  combination  of  the  two 
irritants  can  be  formed. 

If  the  duration  of  such  a  current-shock  is  very  short,  the 
current  must  be  stronger,  if  it  is  to  exercise  any  exciting 
effect  at  all,  than  would  be  necessary  if  the  duration  were 
longer.  It  is  evident  that  a  current,  if  it  lasts  too  short  a 
time,  cannot  effect  a  sufficient  change  in  the  molecular  con- 
dition of  the  nerve,  and  weaker  currents  require  a  longer 
time  to  do  this  than  stronger. 

From  the  curves  in  fig.  73  which  represent  the  duration 
of  inductive  currents,  it  appears  that  without  exception  the 
commencement  of  the  current  results  more  abruptly  than  its 
disappearance.  The  commencement  of  every  inductive  cur- 
rent must  therefore  more  easily  excite  than  does  its  end, 
especially  as  this  is  always  the  case  even  in  the  ordinary 
closing  and  opening  of  every  constant  current,  in  which  such 
considerable  differences  in  the  duration  do  not  occur.  In 
the  case  of  Aveak  inductive  currents  it  is  always  only  the 
commencement  which  is  active,  in  other  words  an  inductive 
current  acts  as  does  the  closing  of  a  continuoiis  current. 
ISTow  let  us  suppose  that  an  inductive  current  is  passed 
throusfh  a  nerve  in  an  ascending  direction.     So  long  as  the 


NOTES    AND    ADDITIONS.  309 

current  does  not  exceed  a  certain  strength,  it  can  excite ; 
but  when  it  is  strong  it  is  ineifective,  since  the  closing  of 
strong  ascending  currents  is  always  ineffective.  If,  however, 
the  current  is  made  yet  stronger,  it  may  again  become  effec- 
tive, because  the  opening  portion  of  the  current  can  now,  in 
spite  of  its  retarded  course,  cause  an  irritation.  This  gap 
{Liicke)  in  the  action  was  observed  by  Tick,  and  afterwards 
by  Tiegel.  How  far  other  causes  besides  those  here  ex- 
plained combine  to  produce  this  peculiar  phenomenon,  we 
cannot  examine  further  here. 


8.  Action  of  Tkansverse  Currents.    Unipolar  Irritation 
(p.  152). 

If  a  curient  is  passed  transversely  through  a  nerve,  that 
is,  in  a  direction  at  right  angles  to  the  long  axis  of  the  nerve 
fibres,  it  has  no  effect.  To  effect  the  alteration  in  the  posi- 
tion of  the  nerve  molecules  which  we  regard  as  the  cause 
of  the  process  of  excitement,  the  current  must,  therefore, 
pass  in  the  longitudinal  direction  of  the  nerve.  This  is  pro- 
bably due  to  the  peculiar  electric  forces  of  the  nerve-par- 
ticles, which  ai-e  treated  of  in  detail  on  page  215  et  srq.  Just 
as  an  electric  current  if  it  flows  pai-allel  to  a  magnetic  needle 
deflects  the  latter,  but  has  no  such  effect  when  it  flows  in  a 
direction  at  right  angles  to  that  of  the  needle,  so  the  nerve 
particles  can  only  be  distui-bed  from  their  quiescent  position 
by  currents  which  run  parallel  to  the  axis  of  the  nerve.  If 
the  cvirrent  is  directed  obliquel}*  to  the  nerve  fibre,  it  acts 
but  not  so  strongly  as  when  it  is  parallel,  and  the  degi'ee  of 
the  action  decreases  proportionately  as  the  angle  which  the 
current  makes  with  the  nerve-fibre  approaches  more  nearly 
to  a  right  angle. 

The  connection  between  the  phenomena  of  electrotonus 
and  excitement  of  the  nerve  led  us  to  believe  that  the  excite- 
ment takes  place,  not  throughout  the  whole  portion  of  the 
nerve  traversed  by  the  current,  but  only  in  a  part  which  on 


310  PHYSIOLOGY    OF   MUSCLES   AND   NERVES. 

closing  is  near  the  kathode,  on  opening  is  near  the  anode. 
This  gives  rise  to  the  question,  whether  it  is  possible  to 
expose  the  nerve  to  the  action  of  one  electrode  alone.  This 
may  be  done,  in  the  case  of  men  or  other  animals,  by  placing 
one  electi'ode  on  the  nerve,  the  other  on  a  remote  part  of 
the  body.  If  the  kathode  is  situated  on  the  nerve,  only 
closing  pulsations  are  obtained ;  if  the  anode  is  situated  on 
the  nerve,  opening  pulsations  are  alone  observed.  If  the 
currents  are  very  powerful,  excitement  may  certainly  occur 
at  the  point  where  the  nerve  meets  the  adjacent  tissiies. 
This  form  of  nerve  irritation  may  be  called  unipolar,  though 
in  a  different  sense  from  that  in  which,  the  name  is  usually 
used  in  cases  where  only  one  wire  is  laid  on  the  nerve,  and 
yet  currents  may  flow  through  the  nerve.  Such  cases,  how- 
ever, are  physiologically  of  no  special  interest. 

9.  Takgent  Galvanometer  (p.  162). 

In  the  ordinary  tangent-galvanometer  a  small  magnetic 
needle  is  placed  in  the  centre  of  a,  conjparatively,  A^ery  large 
circle,  thi-ough  the  periphery  of  which  the  current  is  made  to 
pass.  When  the  needle  is  deflected,  the  position  of  its  poles 
does  not  alter  essentially  as  regards  the  current,  the  action  of 
which  may  therefore  be  regarded  as  directly  propoitionate  to 
its  strength;  and  from  the  opposed  action  of  the  current, 
and  of  the  force  of  attraction  wliich  the  earth  exercises  on 
the  needle,  which  must  also  be  regarded  as  constant,  it  is 
evident  that  the  two  forces  must  be  in  equilibrium,  if  the 
trigonometric  tangent  of  the  angle  of  deflection  is  propor- 
tionate to  the  strength  of  the  current. 

Such  tangent-galvanometers  are,  however,  only  adapted 
for  measuring  powerful  currents.  The  galvanometer  which 
we  have  described,  adapted  for  very  weak  currents,  is  differ- 
ent. But  if,  as  was  assumed,  all  the  deflections  which  are 
to  be  measured  are  but  very  small,  we  may  still  assume  that 
the  mode  of  the  influence  of  the  current  on  the  magnet  is 


NOTES    AND    ADDITIONS.  311 

not  altered  by  the  deflectiou.  Then,  in  the  case  of  this  ap- 
paratus also,  the  strength  of  the  currents  may  be  regarded 
as  proportionate  to  the  tangent  of  the  angle  of  deflection. 
A  glance  at  fig.  19,  on  p.  57,  shows  that  the  displacement 
of  the  scale  is  equal  to  the  tangent' of  the  double  angle  of 
deflection.     For  so  small  an  angle  we  may  put 

tg  (2  u)  =  2  tcj  u, 

that  is  to  say,  the  tangent  of  the  double  angle  is  equal  to 
double  the  tangent  of  the  single  angle.  And  from  this  it 
follows  that  the  strength  of  the  cui-rents  is  proportionate  to 
the  displacement  of  the  scale  directly  observed. 


10.  Tensions  in  Conductoes  (p.  133). 

To  determine  the  absolute  amount  of  tension  at  any 
point  in  a  conductor,  it  would  be  necessary  electrically  to 
isolate  the  conductor,  and  to  connect  the  point  in  question 
with  a  sensitive  electrometer.  But  if  any  point  of  the  iso- 
lated conductor  is  brought  into  conducting  connection  with 
the  surface  of  the  earth,  this  point  would  assume  a  tension 
equal  toO,  without  any  alteration  inthediflTerences  of  tension 
at  the  various  points.  Other  points  of  the  conductor  may 
now  be  brought  successively  into  connection  with  the  earth, 
thus  altering  the  absolute  values  of  the  teiisions  at  the 
separate  points,  though  the  diflference  between  the  tensions  at 
the  various  points  remains  the  same.  From  this  it  follows 
that  these  differences  are  alone  of  importance  for  us.  In  our 
later  explanations  we  have  therefore  represented  the  matter 
as  though  certain  points  (the  boundaries  between  the  longi- 
tudinal and  cross  section)  had  a  tension=0 ;  that  is,  we  always 
thought  of  them  as  connected  with  the  earth.  All  tensions 
that  are  greater  than  this  we  call  positive,  all  that  are  less 
negative. 


312     THYSIOLOGY  OF  MUSCLES  AND  NERVES, 


11.  Duplex  TRANSMIsslo^^    Degeneration,  Regeneration 
AND  Coalescence  of  a  Bisected  Nerve  {p.  218). 

Duplex  transmission  has  been  shown  in  another  way, 
but  the  proof  is  not  so  trustworthy  and  clear  as  that  gained 
by  the  aid  of  negative  variation.  If  nerves  of  the  living 
animal  are  bisected,  a  striking  change  occurs  in  a  very  short 
time  in  the  parts  of  the  nerve-fibre  below  the  point  of  scission. 
The  medullary  sheath  becomes  crinkled,  and  the  excitability 
is  lost.  If,  however,  the  cut  surfaces  are  not  too  far  sepa- 
rated, the  nerve-fibres  can  coalesce,  the  lower  ends  again 
become  excitable,  and  the  excitement  can  be  transmitted 
through  the  cicatrix  thns  formed  in  the  nerve.  On  these 
facts  Bidder  based  an  experiment,  in  which  he  tried  to  cause 
a  sensory  nerve  to  coalesce  with  a  motor  nerve.  The  sen- 
sory nerve  of  the  tongue  (iV^.  lingualis),  a  branch  of  the  fifth 
brain  nerve,  and  the  motor  nerve  of  the  tongue  [N.  hypo- 
(jlossus)  cross  each  other  below  the  tongue  before  they  enter 
the  latter.  If  the  two  nerves  are  cut  at  the  point  where 
they  cross,  and  if  the  upper  end  of  the  sensory  nerA^e,  which 
comes  from  the  brain,  is  connected  with  the  lower  end  of  the 
motor  nerve,  which  enters  the  tongue,  as  much  as  possible 
of  the  two  other  ends  of  the  nerves  being  cut  out,  then  the 
two  different  nerves  coalesce,  so  that  after  a  time  pulsations 
may  be  caused  in  the  muscles  of  the  tongue  by  irritation 
above  the  cicatrix,  and  indications  of  pain  may  be  elicited 
by  irritation  below  the  cicatrix.  The  proof  that  in  this  case 
the  excitement  is  transmitted  downward  in  the  upper  sensory 
nerve,  upward  in  the  lower  motor  nerve,  would  be  unassail- 
able if  it  could  be  shown  that  nerve-fibres  of  the  one  nerve 
1  ave  not  grown  through  the  cicatrix  and  entered  into  the 
other  nerve.  This  possibility,  improbable  as  it  is,  cannot 
be  disproved. 

A  recently  published  experiment  of  Paul  Bert  is  founded 


NOTES   AND    ADDITIONS.  313 

on  a  similar  idea.  Bei-t  made  a  -wound  in  the  Lack  of  a  rat, 
cut  off  a  small  piece  of  tbe  end  of  the  tail,  and  fixed  the  tail 
firmly  in  the  wound  on  the  back.  The  tail  of  the  rat  coa- 
lescing with  the  flesh  of  the  back,  it  was  attached  at  two  points 
like  the  handle  of  a  pot.  The  original  root  of  the  tail  was 
then  cut  through,  so  that  the  attachment  to  the  back  alone 
remained.  If  the  free  end  of  the  tail,  which  was  originally 
the  taU-root  of  the  rat  so  treated,  is  pinched,  the  animal 
feels  it ;  so  that  the  irritation  is  evidently  transmitted  in 
the  sensory  nerves  in  a  direction  opposite  to  that  which  is 
usual  in  the  tail  of  a  rat  under  normal  conditions,  and  it  is 
accordingly  evident  that  the  sensory  nerves  of  the  tail  have 
the  power  of  transmitting  the  excitement  in  both  directions. 


12.  Negative  Yariation  and  Excitement  (p.  220). 

That  negative  variation  is  a  constant  and  inseparable 
accompaniment  of  nerve-excitement  has  been  shown  by 
du  Bois-Reymond  by  a  large  number  of  careful  and  varied 
experiments,  which  have  been  confirmed  and  extended  in 
various  directions  by  many  observers.  It  makes  no  difference 
by  what  iriitant  the  nerve  is  excited ;  and  both  motor  and 
sensory  nerves  ai*e  conditioned  exactly  alike  in  this  matter. 
From  a  large  number  of  experiments  to  select  but  one  of 
peculiar  interest,  I  may  allude  to  the  experiment  recently 
made  with  the  nerve  of  sight.  If  the  eye  is  extracted  and 
prepared  in  connection  with  a  portion  of  the  nerve  of  sight, 
and  if  the  latter  is  suitably  tested  as  to  its  nerve-current, 
and  light  is  then  allowed  to  fall  on  the  eye,  previously  shaded, 
then  the  current  of  this  nerve  exhibits  negative  variation. 

If  ligatures  are  ajiplied  to  a  nerve  so  that  the  excitement 
cjin  no  longer  propagate  itself  from  one  side  to  the  other, 
irritation  of  one  side  causes  no  negative  variation  in  the 
other  side.  This  experiment  is  of  importance  because  it 
aflbrds  a  means  of  proving  with  sufiicient  cerfciinty  that  no 


314  PHYSIOLOGY    OF    MUSCLES    AND   NERVES. 

brancli-currents  of  the  ■  electric  current  used  for  iiTitation, 
which  might  easily  lead  to  errors,  are  preent  in  the  mtil- 
tiplier. 


13.  Electrotonus,     Secondary  Pulsation  effected  by 
ISTerves.     Paradoxical  Pulsation  (p.  221). 

The  reason  why  it  is  impossible  to  examine  the  electro- 
tonus of  the  intrapolar  portions  is  purely  physical.  If  the 
constant  cui-rent  is  transmitted  through  the  portion  a  k 
(fig.  60,  p.  220),  and  two  points  of  this  portion  are  con- 
nected with  the  multiplier,  then  a  part  of  this  current  passes 
through  the  multiplier  itself,  so  that  the  portion  of  the 
nerve  which  is  situated  between^  these  points  is  traversed 
by  a  weater  current  than  are  the  adjacent  portions.  The 
conditions  are  thus  rendered  so  complex  that  it  becomes 
very  hard  to  explain  the  phenomena.  Other  attempts  to 
study  the  character  of  the  intrapolar  region  have  as  yet 
afforded  no  clear  results. 

If  a  nerve  a  is  laid  on  a  nerve  b,  in  the  way  shown  in 
fig.  75,  A,  B,  C,  so  that  the  nerve  h  forms  a  diverting  arch  for 
a  portion  of  the  nerve  a,  and  if  electro  tonus  is  generated  in 
the  latter  by  a  constant  current,  then  the  electrotonic  cur- 
rent passes  through  the  nerve  l>,  and  can  at  its  commence- 
ment and  cessation  (closing  and  opening)  excite  the  nerve  h, 
and  cause  pulsation  in  the  muscle  of  the  nerve.  This  is 
spoken  of  as  secondary  pulsation  from  the  nerve.  By  rapidly 
repeated  closings  and  openings  of  the  circuit,  tetanus  may  be 
elicited.  But  this  secondary  pulsation  is  caused  only  by 
electrotonus  and  not  by  negative  variation,  so  that  it  can 
be  more  easily  brought  about  by  constant  currents  than  by 
inductive  currents.  It  is  thus  distinguished  from  the  secon- 
dary pulsation  effected  by  muscle,  which  was  described  on 
p.  209.  The  negative  variation  of  the  nerve-current  is  too 
weak  to  cause  any  noticeable  efiect  in  a  second  nerve. 


NOTES   AXD   ADDITIONS. 


315 


A  special  form  of  secondaiy  pulsation  effected  through  the 
nerve  has  been  described  by  du  Bois-Eeymond  as  paradoxical 
pulsation.  If  a  constant  cuiTent  is  passed  through  the  bi-anch 
of  the  sciatic  nerve  to  which  allusion  is  made  in  Note  4, 
which  passes  to  the  flexor  muscle  of  the  lower  leg,  then  the 
calf -muscle  may  also  pulsate  when  the  current  is  closed  and 


Fig.  75.    Secondary  pulsation  effected  by  nerve. 

opened.  This  is  an  apparent  exception  to  the  law  of  the 
isolated  transmission  of  the  excitement  {cf.  p.  117);  but 
actually  the  excitement  has  not  passed  from  the  irritated 
fibres  to  the  adjacent  fibres,  but  the  electrotonic  current  of 
the  one  fibre  has  flowed  through  the  neighbouring  fibies  aud 
has  independently  irritated  them. 


14.  Pai?electronomy  (p.  237). 

The  real  causes  of  parelectronomy  and  the   conditions 
under  which  it  is  more  or  less  strongly  developed,  are  as  yet 


316  PHYSIOLOGY    OF    MUSCLES    AND   ]S"ERVES. 

far  from  being  understood.  But  at  any  rate  it  is  impossible 
to  conceive  the  matter,  as  though  tbe  currentless  condition  of 
the  muscles — that  is  to  say,  the  same  tension  on  the  longi- 
tudinal and  transverse  sections — were  normal,  and  as  if  every 
negativeness  on  the  transverse  section  were  the  result  of 
injury.  For  all  possible  degrees  of  j)arelectronomy  are  to  be 
found — even  the  reversed  order,  in  which  the  cross-section  is 
more  positive  than  the  longitudinal  section — in  uninjured 
muscles  ;  while  in  other  cases  the  ordinary  muscle-current 
is  found  powerfully  developed  in  quite  uninjured  muscles. 
Moreover,  as  we  have  stated  in  the  text,  the  question  whether 
differences  of  electric  tension  occur  in  uninjured  muscle  has 
no  bearing  on  the  question  whether  electromotive  forces  are 
present  within  the  muscle.  We  declare  ourselves  in  favour 
of  this  hypothesis,  because  it  most  simply  and  easily  explains 
all  the  phenomena.  We  also  apply  it  to  structures  on 
the  outer  suiface  of  which  it  can  be  proved  with  certainty 
that  no  differences  of  tension  are  present,  as  in  the  electric 
plates  of  fishes.  Por  this  assumption  we  have  the  same 
grounds  on  which  physicists  rely  in  claiming  the  existence  of 
molecular  magnets  in  every,  even  quite  unmagnetic  piece  of 
iron.  l^Hiatever,  therefore,  may  be  the  true  explanation  of 
parelectronomy,  it  cannot  essentially  affect  our  well-founded 
conception  of  the  electric  forces  of  muscles.  If,  however, 
du  Bois-Ile}Tnond's  supposition  is  confirmed,  that  the  pulsa- 
tions which  occur  during  life  leave  behind  them  an  after- 
effect on  the  muscle-ends,  which  makes  the  latter  less  nega- 
tive, some  approacli  woukl  be  made  to  an  explanation  of  the 
phenomenon. 


15.  Discharge  Hypothesis  akd  Isolated  Teansmissiox 
IN  THE  Nerve-Fibre  (p.  249). 

The  explanation  of  the  fact  that  the  processes  of  ex- 
citement remain  isolated  in  a  nerve-fibre  without  passing 
into  adjacent  nerve-fibres,  ajjpears  the  more  inexplicable,  if 


NOTES    AND    ADDITIONS.  317 

we  regard  these  processes  as  electric,  in  that  tlie  separate 
fibres  are  not  electrically  isolated  from  each  other.  But 
the  explanation  which  we  gave  of  the  isolated  excitement  of 
but  one  muscle-fibre  by  a  variation  of  the  electric  current  in 
the  appropriate  nei-ve,  also  explains  isolated  transmission  in 
the  nerve-fibres.  For  if  the  electrically  active  parts  are 
very  small,  comparatively  powerful  electric  action  can  take 
place  in  them,  and  yet  the  current  may  be  quite  unobserv- 
able  at  a  little  distance.  This  is  a  consequence  of  the  law 
of  the  distribution  of  currents  in  irregular  conductors, 
explained  in  chapter  x.  §  2.  We  must,  therefore,  assume 
that  the  electrically  active  particles  situated  in  the  axis  of 
a  nerve-fibre  aie  small  in  comparison  with  the  diameter  of 
the  fibre,  aud  that  therefore  their  effect  at  the  outer  surface 
of  the  fibre  is  already  so  weak  that  it  cannot  act  and  cause 
irritation  in  an  adjacent  fibre.  In  Note  13  we  have  seen 
that  no  action  takes  place  by  negative  variation  from  one 
fibre  on  an  adjacent  fibre.  Our  multipliers  are  much  more 
sensitive  than  nerve-fibres,  so  that  the  separate  negative 
variations  during  the  tetanisation  of  the  nerve  can  combine 
their  action  on  the  multiplier  ;  but  this  is  impossible  in  the 
case  of  the  excitement  of  nerve-fibres. 


INDEX. 


ABS 
A  BSOLUTE  force  of   muscles, 
■^    67,  G8 

Acid,  formation    of,  in  muscle, 

73,87 
Activity    of    muscle,    37,     202, 

235 ;  of  nerve,  107,  216 
Adamkicxewicz,  76 
Adequate  irritants,  285 
Aeby,  100 

Albuminous  bodies,  73,  SO 
Ammonia,  257 
Amoehce,  6 

Amoeboid  movements,  7 
Anelectrotonus,  129,  111 
Animal,  5 
Anode,  128,  220 
Arches,  diverting  homogeneous, 

177,  181 
Akistotle,  155,  285 
Ascending  currents,  131: 
Attachment  of  muscles,  17 
Automatic  movement,  271 
Avalanches,  250 
Avalanche-like  increase  in  the 

excitement    of    nerves,    122, 

300 
Axis-band,  104 
Axis-cylinder,  104 


IMCON  as  food,  85 
■^     Ball-sockets,  l'.»,  93 


Beclard,  73 
Beknard,  253 


CHE 

Beexstein,  100,  219 

Bert,  312 

Blood,  78,  273 

Blood-corpuscles,  7 

Blood-vessels,  96,  272 

DU  Bois  Eeymond,  25,  30,  35, 
36,  53,  59,  73,  87,  111,  150, 
156,  165,  181,  183,  186,  205, 
208,  217,  230.  248,  278,  313, 
315,  316 

Bones,  17,  IS,  93 

Branched  muscle  fibres,  101 

Branching  of  electric  currents, 
132,  150 

Brownian  movements,  3 

Brijcke,  89 

Burden,  23,  39,  64 

BuEDOX- Sanderson,  223 


rULF-MUSCLE.      Sec   Gastro- 

^     cnemius 

Carbonic  acid,  formation  of,  in 
muscle,  42,  73,  81 

Carrying-height  (Traghche)  41 

Cells,  9.    Si^e  also  Nerve-cells 
I   Central-organ  of     the    nervous 
j       system,  ~i03,  117,  265 
I   Centrifugal      and      centripetal 
{       nerves,  266 
I   Cerebrum,  277 
■   Chamois-hunters,  85 
j   Chemical   composition   of   mus- 
!       clcs,  73 


320 


INDEX. 


Chemical  irritants,  30,  109,  257 
Chemical  processes  in    miiscle, 

42,  73 
Ciliary  cells,  10 
Ciliary-movements,  10 
Circuit,  electric,  159,  165 
Claudius  Claudtanus,  155 
Closing  of  a  current,  32,  132,  30i 
Closing  inductive  current,  151, 

299 
Combination    of  tensions,   228  ; 

of  irritants,  299 
Compensation,  183 
Compensator,  round,  186    . 
Conception,  279,  286 
Conine,  253 

Conscious  sensation,  277 
Conservation  of  energv,  77 
Constant  currents,  34,"  109,  126, 

131 
Correlative  action,  270 
Correlative  sensation,  276 
Creatin,  74 
Cross-section  of  the  muscle,  66, 

190,  198,  203,  236,  256 ;  of  the 

nerves,  120,  216,  256 
Curare,  253 
Current-curves,  1 78 
Current-planes,  179 
Curve  of  excitability,  121,  300 

TjARWIN,  224 

-^     Death  of    the    muscle,   86, 
207  ;  of  the  nerve,  120,  124 

Death-stiffness-,  87 
Degeneration  of  a  cut  nerve,  312 
Descending  currents,  134 
Bio  nee  a  vivscijnila,  149,  224 
Discharge-hypothesis,  248,  316 
Discs  of  muscle-fibres,  14 
Disdiaclasts,  15,  102 
Dislocation  of  the  neck,  273 
Diverting  arches,  177 
Diverting  cylinders,  181 
Diverting  vessels,  166 
Division  of  electric  currents,  132, 
170 

DONDEES,  289 

Dorsal  marrow,  106,  277 


FIB 

Double  refraction,  15 
Duplex  transmission,  217,  312 
Dynamite,  251 
Dj'namometer,  69 

■pLASTICITT,  21 ;  alteration  of, 
^  on  contraction,  44,  70 ;  co-ef- 
ficient of,  23  ;  law  of,  22 
Electric  current,  159 
Electric  eel,  156 
Electric  fishes,  154,  222,  227,  241 
Electric  irritation,  32,   109,  149 

151 
Electric  organs,  158,  222 
Electric  plates,  158,  222,  227,  241 
Electric  ray,  156 
Electric  wheel,  33 
Electrodes,  128 ;    unpolarisable, 

181 
Electromotive  force,  168,  232  ;  of 

the  muscles  and  nerves,  153, 

et  seq. 
Electromotive  surface,  179,  227 
Electrotonus,  127,  139,  220,  238, 

309,  314 
Element.      See   Muscle-element 

and  Nerve-element 
Elementary  organisms,  8 
Energy,  U,  50,  64,  72,  77  ;  spe- 
cific, 286 
Engelmakn,  100 
Equipoise,  unstable,  250 
Equator,  electromotive,  190 
Ermann,  45 
ExcitabiUtA-,  119,  122,  126,  299, 

300 
Excitement,  126,  141,  150,  151, 

313 
Exhaustion,  79,  121 
Extension,  21,  92,  295  ;  gradual, 

24 
Extrapolar  regions,  220 

"PARADAT,  156 

-*-      Feet  of  the  diverting  arch, 

176 
Fibres.     See   Muscle-fibres   and 

Nerve-fibres 
Fibre-cells,  96 


INDEX. 


321 


Fibrillie,  U 

FiCK,  41,  299,  309 

Fish,  electric,  154,  222,  227,  241 

Flat-bones,  18 

Flesh,  2,  11,  86 

Force,  electromotive,  168,  232 

Force,  muscular,  50,  67 

Forms  of  muscles,  91 

Form,    changes    of,    in    muscle 

during  contraction,  45 
Freeing  of  forces,  249 
Function,  293 

AALVAXOMETER,  160 

^  Ganglion-cells.  See  Nerve- 
cells 

Ganglion-balls.     See  Nerve-cells 

Gaatroenemius,  17,  67,  109,  199, 
200,  203,  209,  302 

Gauss,  58 

Gerlach,  246,  247,  259 

Gizzard,  96 

Glands,  212,  227,  262 

Glycerine,  257 

Glycogen,  73,  80,  87 

Goethe,  285 

Graphical  representation,  293 

s'Geavesande,  23 

Grey  nerve-fibres,  104 

Gunpowder,  250 

Gijmnotus,  156 

TJALLER,  252 
-'-'■     Hallucination,  279 
Harlesr,  253 
Head  of  muscle,  1 3 
Heart,  the,  101,  210 
Heidenhatn,  76,  146 
Height  of  elevation,  37,  2;t7 
Helmholtz,  50,  52,  59,  73,  75, 

115,  228,  287,  290,  306 
Hermann,  70,  100 
Hinge-socket,  19,  93 
HiRSCH,  288 
Homogeneity  of  all  nerve-fibres, 

263 
Hook,  23 
Humboldt,  156 
Hypotheses,  229,  234 
15 


mag 

TNCREASE    in     thickness     of 
-^     muscle  on  contraction,  44 
Induction,  magnetic,  243 
Inductive  currents,  31,  110,  139, 

304,  308 
Induction  coil,  31,  35,  119,  306 
Inertia  of  consciousness,  290 
Inosit,  74,  87 
Internal  work  during  tetanus,  41, 

76,77 
Intestine,  96,  272  ;  of  the  tench, 

101 
Intrapolar  regions,  129,  221 
Involuntary  movements,  271 
Irregular  movements,  272 
Irritants.  30,  109 
IiTitability,  30, 108 ;  independent, 

255 
Isolated    transmission     in     the 

nerve-fibre,  117,  315 
Isoelectric  curves.    See  Tension- 
lines 


r'ATELECTROTONUS,129,141 

•^     Kathode,  128,  220 

Kernel  (nucleus)  5,  7,  11,  16,  96, 

105 
Key,  tetanising,  36 
Kleistian  jar,  30 
Kolliker,  253 
Kronecker,  299 
Kt'HNE,  89,  256,  257 


T  ABOUR  accumulator,  41 

^     Lactic  acids,  73,  80,  87,  258 

Latent  irritation,  56,  64 

Law  of  eccentric  sensation,  280 

Law  of  pulsations,  13.5,  142 

Leverage  of  bones,  93 

Leyden  jar,  30 

Life  centres,  272 

Light,  15,  284 

Long  bones,  IS 


M 


AGNET,  compared  to  muscle 
and  nerve,  147,  230,  260 


322 


INDEX. 


Malaptcrurus,  156 

Mateucci,  229 

Mechamcal  irritants,  30,  109,146 

Medullary  sheath,  104,  245,  254, 
«63 

Mimosa  jJudica,  2,  224 

Mirror,  reading  of  small  angles 
by  means  of,  57,  162 

Moditication  of  excitability,  131, 
143 

Molecular  hypothesis,  238 

Molecular  movement,  3 

MoUusca,  102 

3Io)-myrus,  159. 

Motor  nerves,  261 

Movement,  1 ;  in  jilants,  2,  8, 
224 ;  of  the  smallest  organisms, 
4 ;  molecular,  3 ;  protoplas- 
mic, 6 ;  amoeboid,  6 ;  ciliary, 
9 ;  muscular,  9  et  seq. ;  peri- 
staltic, 98,  272  ;  voluntary 
and  involuntary,  98,  275  ;  au- 
tomatic, 273  ;  rhythmic,  272  ; 
tonic,  272 

MiJLLER,  285 

Multiplier,  161 

MuNK,  116,  224,  300 

Muscle,  2,  11,  12  et  seq.,  189  et 
seq.,  226  et  seq. 

Muscle-current,  191,  202,  226 

Muscle-element,  232,  239 

Muscle-fibre,  striated,  14,  45,  96, 
245  ;  smooth,  96,  101 ;  zigzag 
arrangement  of,  14 

Muscle-fibre  pouch.  See  Sarco- 
lemma 

Muscle-fluid,  88 

Muscle-prism,  189,  230,  234 

Muscle-rhombus,  193,  195,  230 

Muscle-note,  43,  211 

Muscle-telegraph,  30 

Myograph,  26,  37,  52,  100,  111 

Myosm,  74,  90 


l^ASSE,  73 

-'-'    Negative  variation,  203,  210, 

214,  216,  226,  235,  313 
Nerve-cells,  103,  266,  269 


POL 

Nerve-centres.  See  Central  Or- 
gans. 

Nerve-current,  215,  226,  236 

Nerve-element,  237  et  seq. 

Nerve-fibres,  103  et  seq. ;  termi- 
nation of,  in  muscles,  245 

Nerve-net,  246 

Nerve -processes,  107,  265 

Nerve-sheath,  104,  111 

Nerve,  terminal  plates  of,  245 

Nervous  system,  103 

Nettle,  stinging,  movements  in 
hairs  of,  8 

Newilemma.    See  Nerve-sheath 

Neutral  point,  129 

Nicotin,  253 

Nitroglycerine,  250,  251 

Nucleolus,  105 

Nutriment  of  labourers,  82 

Nut-socket,  19,  93 


APENING  of  a  current,  32, 131, 

^     308 

Opening  induction-current,  150, 

304 
Opening-tetanus,  132,  143 
Oppian,  155 
Organs.    See  Central  Organs  and 

Electric  Organs 
Over-bm-den,  65 
Oxidation,  process  of,  in  muscle, 

42 


PARADOXICAL  pulsation,  314 
^     Parelectronomy,208,236,315 
Penniform  muscles,  91,  199 
Peripheric  nerves,  103,  107 
Peristaltic  movement,  98,  272 
Pflugee,  122,  140 
Physiological  time,  288 
Plants,  movements  of,  2,  9,  224  ; 

electric  action  of,  153,  223  et 

seq. 
Plates,  electric,  158, 222, 227,  241 
Pliny,  155 
poggendoef,  183 
Polarised  light,  15 


I]S'DEX. 


323 


PEE 

Prevost  and  Dctmas,  45 
Prism.     See  Musde  Prism 
Propagation,    of    the    pulsation 
■within   the  mascle-fibre,   99; 
of   the    irritation  within  the 
nerve-fibre,  110,  114,  287;  of 
the  negative  variation  in  the 
nerve-tibre,  129 
Protoplasm,  5 
Protoplasmic  movement,  6 
Protoplasmic  processes,  106 
Pulsation,  31.  56,  210 ;  secondary, 
210,  314;  law  of,  135,  142,299 


pADIATIOX  of  sensations,  276 
-'-''     Eate   of  excitement  in  the 
nerve-fibre,  98 ;  of  transmission 
within  the  nerve-fibre,  110, 1 1 4, 
129, 287 
Reaction  in  muscles,  87 
Eeceptive  apparatus  of  sensory- 
nerves,  283 
Reflection,  290     - 
Reflex  actions,  274,  290,  301 
Respiratory  movements,  272 
Respiratory  centre,  272 
Rest  of  muscles,  37 
Retardation  (^Hemvuinri'^,,  80 
Retardatory  nerves,  263 
Rheochord,  133,  149,  184 
Rhombus.    See  Muscle-rhombus 
Rhythmic  movements,  272,  281 
Ritter's  tetanus,  132,  143 


OARCOLEMJ/A,  16, 101,  233 
^    Schwann,  70 
Secretory  nerves,  213,  262 
Secondary  pulsation,  210,  314 
Secondary  tetanus,  211 
Semi-penniform  muscles,  91 
Sensation,  1,  262 
Sensitive  machines,  251 
Sensitive  plant,  2 
Shaft  of  a  bone,  19 
Short  bones,  1 8 
Shortening  of  muscles  12.  28 


Skeleton,  muscles  of,  13 

Skin-currents,  207,  213 

Sliding  inductive  apparatus,  35, 

119' 
Smooth  muscle-fibres,  12,  96,  206 
Sockets,  19,  93 
Source  of  muscle-force,  42 
Specific  energies,  286 
Specific  warmth,  76 
Steam    engine,    comparison    of, 

with  muscle,  82 
Stinging-nettles,  movements  in 

hairs  of,  8 
Steauss,  290 
Striated  musc^.e,  11  et  seq. 
Sugar,  73,  80,  85 
Surface,  electromotive,  179,  227 


TAIL  of  muscle,  13 

Tangent  galvanometer,  162, 

310 
Temperature,    influence    of,    on 

muscles  and  nerves,  86,  124 
Tench,  101 
Tension,  electric,  168,  171,  229, 

311 
Tension-curves,  179,  190 
Tension,  ditferences  of,  182,  311 
Tension-lines,  179,  190 
Tension-surfaces,  179 
Terminal   apparatus   of    nerves, 

262,  267 
Tetanus,  34,   37,  41,    109,    300; 

secondarj-,  211,  314 
Tliermic  irritants,  109 
Thermo-electricity,  74 
TiEGEL,  300,  309 
Time,  measurement  of,  51,  61,  98, 

111,  115,  131,288 
Tonic  contraction,  272 
Tm'pedo,  155,  158 
Transmission,  in  the  nerve-fibre, 

110,  141,  287  ;   isolated,  117, 

316  :  duplex,  217,  312 
Transverse  currents  through  the 

nerves,  309 
Trunk  of  a  muscle,  13 


324 


INDEX. 


UNI 

TJNIPOLAR-irritation,  309 

Unpolarisable  electrodes,  181 
Urinary  duct,  100 
Urea,  80,  84 

yASO-AIOTOR  nerves,  261 
'      Yolume  of  muscle,  45,  66 


WAGNER'S  hammer,  34,  306 
''     Warmth  equivalent,  76,  81 


WOR 

Warmth,  generation  of, in  muscle, 
42,  73,  74  ;  in  nerve,  123 

Weber,  45,  263 

Weiss,  73 

Whip-cell  movement,  11 

AVill,  270,  290  ;  deflection  of 
magnetic  needle  by,  205 

Woodcutters,  TjTolese,  85 

Work  accomplished  by  the 
muscle,  37,  38,  72,  76,  296 


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